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Article

Screening Snake Venoms for Toxicity to Tetrahymena Pyriformis Revealed Anti-Protozoan Activity of Cobra Cytotoxins

by
Olga N. Kuleshina
1,
Elena V. Kruykova
2,
Elena G. Cheremnykh
3,
Leonid V. Kozlov
1,†,
Tatyana V. Andreeva
2,
Vladislav G. Starkov
2,
Alexey V. Osipov
2,
Rustam H. Ziganshin
2,
Victor I. Tsetlin
2 and
Yuri N. Utkin
2,*
1
Gabrichevsky Research Institute of Epidemiology and Microbiology, ul. Admirala Makarova 10, Moscow 125212, Russia
2
Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, ul. Miklukho-Maklaya 16/10, Moscow 117997, Russia
3
Mental Health Research Centre, Kashirskoye shosse, 34, Moscow 115522, Russia
*
Author to whom correspondence should be addressed.
†
Deceased.
Toxins 2020, 12(5), 325; https://doi.org/10.3390/toxins12050325
Submission received: 10 April 2020 / Revised: 12 May 2020 / Accepted: 13 May 2020 / Published: 15 May 2020
(This article belongs to the Special Issue Animal Venoms and Their Components: Molecular Mechanisms of Action)
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Abstract

:
Snake venoms possess lethal activities against different organisms, ranging from bacteria to higher vertebrates. Several venoms were shown to be active against protozoa, however, data about the anti-protozoan activity of cobra and viper venoms are very scarce. We tested the effects of venoms from several snake species on the ciliate Tetrahymena pyriformis. The venoms tested induced T. pyriformis immobilization, followed by death, the most pronounced effect being observed for cobra Naja sumatrana venom. The active polypeptides were isolated from this venom by a combination of gel-filtration, ion exchange and reversed-phase HPLC and analyzed by mass spectrometry. It was found that these were cytotoxins of the three-finger toxin family. The cytotoxins from several cobra species were tested and manifested toxicity for infusorians. Light microscopy revealed that, because of the cytotoxin action, the infusorians’ morphology was changed greatly, from teardrop-like to an almost spherical shape, this alteration being accompanied by a leakage of cell contents. Fluorescence microscopy showed that the fluorescently labelled cytotoxin 2 from cobra N. oxiana was localized mainly at the membrane of killed infusorians, indicating that cytotoxins may kill T. pyriformis by causing membrane rupture. This work is the first evidence of the antiprotozoal activity of cobra venom cytotoxins, as demonstrated by the example of the ciliate T. pyriformis.
Keywords:
snake venom; cytotoxin; protozoa; ciliate Tetrahymena pyriformis; immobilization; membrane rupture
Key Contribution: It was shown for the first time that cobra cytotoxins were demonstrated to kill the ciliate Tetrahymena pyriformis. The toxic effect may occur by rupture of the protozoan’s membrane.

Graphical Abstract

1. Introduction

Snake venoms contain a pool of bioactive compounds acting on many different species. The most studied are the venom effects on the vertebrates, while the effects on invertebrates are much less investigated. As for the action on different groups of invertebrates, there are some data about snake venom toxicity to arthropods [1,2,3], the most active against cockroaches being cytotoxins from cobra venom [1]. Antibacterial properties of snake venoms were also tested [4,5] and some active proteins were identified. It was found that phospholipases A2 [6], L-amino acid oxidases [7] and cathelicidins [8] possess antimicrobial properties. There are also some data about the influence of snake venoms on protozoa [9,10]. Recently the in vivo and in vitro antileishmanial activity of krait Bungarus caeruleus [11] and cobra Naja oxiana [12] venoms was demonstrated. It was also reported that the venom of the cobra Naja nigricollis possessed the capacity to kill Trypanosoma brucei, a parasitic protozoan [13]. Furthermore, a disintegrin isolated from Cerastes cerastes venom exhibited antiparasitic activity on Leishmania infantum promastigotes [14].
Protozoa are a diverse group of single-celled eukaryotic organisms with animal-like behaviours such as motility and predation. Protozoa have been divided traditionally on the basis of their means of locomotion into Flagellates, Amoeboids, Sporozoans and Ciliates. Some protozoa are human parasites, causing life-threatening diseases such as malaria, toxoplasmosis, Chagas disease, leishmaniasis, and several others. Many protozoa are also causative agents of dangerous diseases in domestic and wild animals. Some diseases are shared between species, for example, toxoplasmosis and leishmaniasis affect both humans and animals, while others are specific only for animals. Thus, the ciliates Ichthyophthirius multifiliis and Cryptocaryon irritans, commonly known as ich and marine ich, respectively, are highly pathogenic for fishes. These ciliates are responsible for diseases causing significant economic losses to the global aquaculture industry [15], however options for control of diseases are extremely limited. Other ciliates from the Tetrahymena genus are relatives of I. multifiliis [16]. Tetrahymena spp. are extremely motile free-living organisms, but occasionally they can become parasitic and affect some fish species. Thus, Tetrahymena sp., also known as the guppy-killer parasite, is a main infectious agent of guppies [17]. Recently high mortality due to Tetrahymena sp. infection in laboratory-maintained zebrafish was reported [18].
At the same time some ciliates such as Paramecium caudatum, Tetrachymena, Oxytricha trifallax are model organisms used in molecular biology. The ciliated protozoa Tetrahymena sp. has been used in toxicology for decades as a model organism as well as for environmental research to assess the cytotoxicity of chemicals and environmental pollutants [19]. A conventional colorimetric Tetrahymena assay is based on the reduction of 3-(4,5-dimethyl-2-thiazol-2-yl)-2,5-diphenyl- 2H-tetrazolium bromide (MTT) [20]. However, the competing interaction of MTT with some other chemicals or pollutants present in samples cannot be completely excluded. Recently the method based on counting freely moving T. pyriformis organisms was developed, which did not require any additional chemicals [21].
In this study, using the new method we investigated the effects of snake venoms on ciliate Tetrahymena pyriformis and found that cobra venoms are lethal to this species, the cobra Naja sumatrana venom being the most active. Analysis of this venom demonstrated that the lethal effect was produced by cytotoxins of the three-finger family. Cytotoxins from other cobra venoms were also lethal to the ciliate. Thus, for the first time it was demonstrated that snake cytotoxins have antiprotozoal activity, using the example of the ciliate T. pyriformis.

2. Results

To find new polypeptides toxic to protozoa, venoms of several snake species including krait, vipers and cobras were tested for toxicity to the ciliate T. pyriformis. The method based on automatic registration of moving organisms was used. If ciliates are alive, they move constantly. To estimate the number of living microorganisms, the number of cells that have changed their location during a certain observation time should be counted. This concept is realized in a BioLaT-3.2 instrument that is designed for automated observation and computer-aided fixation of objects in a visual field [21]. We have used the BioLaT-3.2 for automated biotesting of venoms for toxicity to T. pyriformis ciliates.
The venom solution was added to the instrument chamber containing infusorians and the number of moving, i.e., live microorganisms, was counted over 30–60 min. The venoms of seven cobras, five vipers, three pit vipers and one krait species were tested. We have found that only cobra venoms were lethal to T. pyriformis at concentrations of less than 2 mg/mL. Among the venoms of the seven cobra species (N. kaouthia, N. melanoleuca, N. naja, N. nigricollis, N. nivea, N. oxiana, N. sumatrana) studied (Figure 1), those of N. nigricollis and N. sumatrana were the most active (Table 1), killing infusorians at concentration of 0.33 mg/mL in less than 10 min (Figure 1). N. sumatrana venom killed all infusorians in 6 min and was chosen for further studies. It was fractionated using different types of liquid chromatography (Figure 2) and every fraction obtained was checked for toxicity to T. pyriformis (Figure 3 and Figure 4).
One fourth of each fraction was freeze-dried and dissolved in 100 μL of water. One tens of each solution, representing equal portions of the tested fractions, was used for the activity measurement. Among the fractions obtained by gel-filtration of the crude N. sumatrana venom, so called main toxic fraction IV (Figure 2A) was the most active against infusorians killing practically all microorganisms in less than 5 min (Figure 3A,B). A strong decrease in the number of cells at the beginning of experiment (Figure 3A, 10 µL fraction IV) is explained by very rapid cell death which occurred during the probe preparation due to the high concentration of toxins. The fraction V was less active and required more than half an hour to kill all infusorians in a counting well (Figure 3A,B).
Other fractions did not result in the death of microorganisms even after one hour of incubation. The fraction IV containing mostly cytotoxins and neurotoxins was further separated by ion-exchange chromatography (Figure 2B). The most basic fractions 10 and 11 were found to be toxic to T. pyriformis and killed all microorganisms within 15 and 5 min, respectively (Figure 3C). All other fractions obtained after ion exchange chromatography were not toxic at all. The fractions 10 and 11 were further fractionated by reversed-phase HPLC (Figure 2C,D), and the activity of toxins obtained was tested (Figure 4). Toxin in fraction 3 (Figure 2D), referred further as NsIV-11-3, was the most active, while others possessed lower, nevertheless pronounced toxicity to infusorians (Table 2). The toxin from fraction 1 in Figure 2C, referred further as NsIV-10-1, was also fairly toxic (Table 2).
The toxins NsIV-10-1 and NsIV-11-3 were characterized by mass spectrometry. The molecular masses determined for them were 6718 and 6758 Da, respectively. In cobra venoms, cytotoxins and short-chain α-neurotoxins possess molecular masses in this range. To identify the toxins isolated, the proteins were subjected to trypsinolysis and molecular masses of the peptides obtained were determined by MALDI mass spectrometry (Table 3). Comparison of masses determined with those of known toxins revealed the similarity of our toxins to cytotoxins from cobra N. sputatrix venom.
According to mass spectrometry data, toxin NsIV-11-3 was identical to cytotoxin 2a from N sputatrix (UniProtKB accession number Q9PST4). Toxin NsIV-10-1 was very similar to cardiotoxin 5A from N. sputatrix (UniProtKB accession number O73857) with the exception of the fragment 45–50 for which no corresponding mass was found in the mass spectrum of toxin tryptic hydrolysate (Figure 5).
To check if other cobra venom cytotoxins possess toxicity to T. pyriformis, cytotoxins 1 and 2 from N. oxiana as well as cytotoxin 3 from N. kaouthia were tested (Figure 4 and Figure 6).
All these cytotoxins were active against T. pyriformis (Table 2). The highest toxicity was observed for cytotoxin 2 N. oxiana and toxin NsIV-11-3 which killed almost all the cells in only 3–4 min at concentration of about 150 μM. Interestingly, glycosylated cytotoxin 3 N. kaouthia, containing carbohydrate moiety at asparagine 29 was not active in this test (Figure 6).
To get information about a possible molecular mechanism of cytotoxin action on infusorians, the light and fluorescent microscopy was used. The addition of cytotoxin 2 from N. oxiana induced infusorian immobilization followed by strong changes in their morphology (Figure 7A). The teardrop-like form (Figure 7A, control) was transformed to almost spherical one (Figure 7A, 5 min). At a longer time (more than10 min), the leakage of cell content was observed (Figure 7A, 15 min). To localize the cytotoxin binding on the infusorians, the fluorescent analogue of cytotoxin 2 from N. oxiana was used. It was found that a small amount of fluorescent toxin was localized inside cells (Figure 7B, 10 min, fluorescence mode), but the main staining by toxin was observed at the membrane of dead infusorians (Figure 7B, 16 min, fluorescence mode).

3. Discussion

Snake venoms have evolved as a potent weapon for prey immobilization and defense from predators. They comprise complex mixtures of peptides and proteins as well as of non-proteinaceous compounds optimized to act on vital systems in the organisms of the prey or predator. Snake predators are fairly large vertebrate animals and snakes themselves feed on relatively large animals, including vertebrates and arthropods. It was assumed quite reasonable that the main toxic venom components were directed against these animals and the biological effects of venoms were studied mostly on these animals. Data about the action of snake venoms and their components on microorganisms are not so numerous [4,5]. However, some proteins with antimicrobial properties were identified. In particular, they include phospholipases A2 [6], L-amino acid oxidases [7] and cathelicidins [8]. Venoms of several snake species were shown to be toxic to protozoans [9,10,11,12] and identification of proteins manifesting anti-protozoan activity in viperid venoms revealed that phospholipase A2 [22], metalloproteinase [23], L-amino acid oxidase [24] and disintegrin [14] are toxic to different protozoa. For example, BnSP-7 toxin, a catalytically inactive phospholipase A2 from Bothrops pauloensis snake venom, showed activity against promastigote Leishmania amazonensis parasite forms, inhibiting parasite proliferation by 60–70% at toxin concentrations of 50–200 μg/mL 96 h after treatment [22]. However, the data about influence of cobra venom on protozoa were very limited. Thus, it was shown that N. haje venom exerted a significant growth inhibition of Trypanosoma cruzi and Leishmania donovani infantum parasites [25] and the venom of N. oxiana revealed remarkable anti-leishmanial effects [12].
It should be noticed that protozoa are not only human parasites, causing life threatening diseases in humans, but they are also pathogens of serious diseases in wild and domestic animals producing substantial losses in agriculture. In particular, the ciliates Ichthyophthirius multifiliis and Cryptocaryon irritans, highly pathogenic for fishes, have been mentioned above [15].
To get more information about the anti-protozoan activity of cobra venoms we have used infusorian T. pyriformis as a model organism. The survival of animals was monitored using an original method [21] in which the mobility of each organism was registered separately and dead unmoving organisms were not registered. Among several snake species (vipers, kraits, and cobras) studied, only cobra venoms were found to be lethal to infusorian T. pyriformis. The venoms of seven cobra species (N. kaouthia, N. melanoleuca, N. naja, N. nigricollis, N. nivea, N. oxiana, N. sumatrana) were tested (Figure 1) to choose the most active one. The highest activity was manifested by the venoms of N. nigricollis and N. sumatrana, and that of N. sumatrana was chosen for the further studies. To identify the active compound, this venom was fractionated by three different types of liquid chromatography (Figure 2), and the activity of each fraction obtained was determined (Figure 3 and Figure 4). As a result several toxins active agains T. pyriformis were isolated. The structures for the most active ones were characterized in detail by MALDI mass spectrometry, and it was shown that these are cytotoxins of the three-finger toxin family. It should be mentioned that in protein data banks there were no amino acid sequence data for toxins from N. sumatrana. The paper on the proteomic characterization of N. sumatrana venom contains only fragmentary data on the cytotoxin amino acid sequences and does not allow the toxin assignment [26]. Recently de novo venom-gland transcriptomics of N. sumatrana from West Malaysia was conducted using next-generation sequencing technology [27]. The transcripts encoding toxin identical to cytotoxin 2a from N. sputatrix were the most abundant among the all transcripts identified. According to MALDI mass spectrometry data, one of the toxins isolated in this work was identical to cytotoxin 2a and the other one was very similar to cardiotoxin 5A from N. sputatrix venom.
Earlier we have studied the interaction of several cytotoxins and their fluorescent analogues with artificial membranes [28] and mammalian cell lines [29]. These toxins including cytotoxins 1 and 2 from N. oxiana as well as cytotoxin 3 from N. kaouthia were tested on infusoria (Figure 4 and Figure 6). All cobra cytotoxins used in this study were toxic to the infusorians, cytotoxin 2 N. oxiana being the most active. The higher activity of N. sumatrana venom as compared with that of N. oxiana may be explained by higher cytotoxin content in the former. To get some information about possible interacting site in cytotoxin, we tested the activity of glycosylated cytotoxin 3 N. kaouthia containing carbohydrate moiety at asparagine 29. Earlier we have shown [30] that this post-translational modification resulted in decrease of the cytotoxic activity of the glycoprotein towards HL60 cells by about two orders of magnitude. This toxin was completely inactive against infusoria (Figure 6), which means that the central toxin loop containing asparagine 29 is involved in the anti-protozoan activity.
It should be mentioned that according to differences in the amino acid sequences of cobra cytotoxins within the so-called central loop II, they can be classified into two groups: P-type and S-type. P- and S-types differ by the presence of either Pro-31(30) or Ser-29(28) residues, respectively [31]. The difference in biological activity between these two types was observed pointing to the more efficient interaction of P-type cytotoxin with membrane [28,32]. The cytotoxins studied in our work belong to different types; CX2 N. oxiana and NSIV-11-3 are of P-type whereas CX1 N. oxiana, CX3 N. kaouthia and NSIV-10-1 are of S-type (Table 2). Based on a comparison of toxicity for ciliates, a very cautious conclusion can be drawn that the p-type exhibits higher toxicity (Table 2). However, in order to make a more rigorous conclusion, additional experiments with a large number of toxins are required.
To establish a possible mechanism of the cytotoxin action, the light and fluorescence microscopy studies were performed: they showed that, due to the cytotoxin action, the morphology of infusorians changed greatly from teardrop-like to almost spherical shape. If incubation with the cytotoxin was continued for the longer time (more than 10 min), the leakage of cell content was observed (Figure 7). Fluorescently labelled cytotoxin 2 N. oxiana was found to be localized mainly at the membrane of dead infusorians, however it was also visible in lesser amount inside the infusorians. These data suggest that cytotoxins kill T. pyriformis by membrane rupture.
As discussed in the Introduction, Tetrahymena spp. in some cases can become parasitic and affect certain fish species. Thus, it can seriously infect guppies and is thus called the guppy-killer parasite [17]. Moreover, Tetrahymena sp. infection was reported for laboratory-maintained zebrafish [18]. Interestingly, the most active cytotoxins (e.g., CX2 N. oxiana) kill Tetrahymena in less than 5 min at concentration of 1 mg/mL while LD50 for cytotoxin of the cobra Naja mossambica mossambica to fish Aphanius dispar Ruppell (Pisces, Cyprinodontidae) was about 0.4 mg/mL at external application to the surrounding water [33]. Lethality, based on complete fish immobility, was determined after 60 min. It is quite possible that Tetrahymena might be killed much faster at this toxin concentration. Thus, cytotoxins may be considered as a possible treatment for fishes infected with Tetrahymena. However, this suggestion needs further experimental studies.

4. Conclusions

The venoms of snakes from several genera were tested for toxicity to protozoa T. pyriformis. The cobra venoms were found to possess the highest activity and N. sumatrana venom was the most active. The targeted isolation of toxic polypeptides resulted in purification of cytotoxins belonging to three-finger toxin family. The cytotoxins from other cobra venoms were active against T. pyriformis as well. Thus, using the ciliate T. pyriformis as an example, for the first time we have shown that cobra venom cytotoxins have antiprotozoal activity.

5. Materials and Methods

All salts obtained from local suppliers were of analytical grade or higher. Cytotoxins from N. oxiana venom were purified as described [29] and cytotoxin 3 and its glycosylated form were isolated from N. kaouthia venom as described [30]. Fluorescently labeled cytotoxin II from N. oxiana was prepared as described [34]. Acetonitrile was purchased from Kriochrom (Sankt Petersburg, Russia), and trifluoroacetic acid from Merck KGaA (Darmstadt, Germany).

5.1. Snake Venoms

Cobra (N. kaouthia, N. melanoleuca, N. naja, N. nigricollis, N. nivea, N. oxiana, N. sumatrana) and viper (Vipera nikolskii, V. ursinii, Macrovipera lebetina, Bitis arietans, Echis multisquamatus) venoms were obtained as described earlier [30,35]. The krait Bungarus fasciatus venom was obtained as described in [36]. Venoms collected were dried over anhydrous CaCl2 and stored at −20 °C until use. Venoms of Agkistrodon contortrix contortrix, Calloselasma rhodostoma and Gloydius blomhoffii were a kind gift of Professor T. Morita (Meiji Pharmaceutical University, Tokyo, Japan).

5.2. Anti-Protozoan Activity Measurements

Anti-protozoan activity was measured on the ciliate T. pyriformis using a BioLaT-3.2 instrument operating under the AutoCiliataXP program (Europolytest Ltd., Moscow, Russia) essentially as described [21]. T. pyriformis (strain WH14 from the collection of the Russian Research Institute of Veterinary Sanitary, Hygiene and Ecology, Moscow, Russia) was cultivated in the medium containing 0.5% pancreatic casein hydrolysate (Merck KGaA), 0.5% glucose, 0.1% Springer 0251 yeast extract (Bio Springer, Maisons-Alfort, France) and 0.1% NaCl. For the activity determination, the solution tested (5 to 50 μL) was added to the suspension of T. pyriformis cells in measuring wells of the instrument, and the number of survived cells was counted each minute using the AutoCiliataXP program for a period of up to 1 h. In brief, the wells were positioned under two video cameras and the survived cells were cyclically counted. The real time dependences of the number of survived cells on the time were shown on the display. Only number of moving cells at each minute was counted. At the end of experiment all the data were saved as an Excel file.

5.3. Venom Fractionation

Gel filtration was performed on a SuperdexTM 75 column (10 × 300 mm, Cytiva, Marlborough, MA, USA), equilibrated with 0.1 M ammonium acetate (pH = 6.2), at a flow rate of 0.5 mL/min. The eluting proteins were detected by absorbance at 280 nm. In total 63 mg of Naja sumatrana venom were fractionated. The fractions were pooled as shown by horizontal bars in Figure 2A, freeze-dried and analyzed for lethal activity against T. pyriformis. For this purpose, each freeze-dried fraction was dissolved in 500 µL of water, 120 µL of this solution was freeze-dried again to remove ammonium acetate and the dried residue was dissolved in 100 µL of water for toxicity measurement. From 1 to 10 µL of the solution was added to the measuring well of BioLaT-3.2 instrument containing 600–1000 infusorians in 300 µL of the medium and the number of surviving organisms was registered for up to 1 h. The faction IV (Figure 2A) toxic to T. pyriformis was separated by ion-exchange chromatography on a HEMA BIO 1000 CM column (8 × 250 mm, Tessek, Prague, Czech Republic) with a gradient of 5–700 mM ammonium acetate (pH 7.5) in 140 min, at a flow rate of 0.5 mL/min. Fractions obtained (Figure 2B) were further screened for lethal activity as described for gel-filtration fractions and toxic fractions 10 and 11 were further separated by reversed-phase chromatography on a Bio Wide Pore C18 column (10 × 250 mm, Merck KGaA) in a gradient of acetonitrile 20–50% in 60 min in the presence of 0.1% trifluoroacetic acid, at a flow rate of 2.0 mL/min.

5.4. Mass Spectrometry and Peptide Mass Fingerprinting

MALDI mass-spectrometry and peptide mass fingerprinting were performed as described [37].

5.5. Microscopy

The microscopy studies were performed using an IX-71 inverted microscope operating under the CellA program (Olympus Corporation, Tokyo, Japan). The suspension of T. pyriformis cells in the cultivating medium (40 µl) was placed to the Greiner flat bottom 96-well plate (Merck KGaA) and the solution of cytotoxin 2 N. oxiana or rhodamine labeled cytotoxin 2 from N. oxiana were applied to final concentration of 1 mg/mL. Images were captured at the certain time intervals at automatic exposure time in the visible light or in fluorescence mode using the U-MNG fluorescence cube (excitation at 530–550 nm). Fluorescent images were taken first.

Author Contributions

Conceptualization, O.N.K., L.V.K. and Y.N.U.; methodology, E.G.C.; investigation, O.N.K., E.V.K., T.V.A., A.V.O., R.H.Z.; resources, E.G.C., V.G.S. writing—original draft preparation, O.N.K., L.V.K.; writing—review and editing, L.V.K., Y.N.U., V.I.T.; supervision, V.I.T.; project administration, Y.N.U.; funding acquisition, V.I.T., Y.N.U. All authors have read and agreed to the published version of the manuscript.

Funding

The reported study was funded by RFBR according to the research project 18-54-54006.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Starkov, V.G.; Osipov, A.V.; Utkin, Y.N. Toxicity of venoms from vipers of Pelias group to crickets Gryllus assimilis and its relation to snake entomophagy. Toxicon 2007, 49, 995–1001. [Google Scholar] [CrossRef] [PubMed]
  2. Richards, D.P.; Barlow, A.; Wuster, W. Venom lethality and diet: Differential responses of natural prey and model organisms to the venom of the saw-scaled vipers (Echis). Toxicon 2012, 59, 110–116. [Google Scholar] [CrossRef]
  3. Saviola, A.J.; Gandara, A.J.; Bryson, R.W., Jr.; Mackessy, S.P. Venom phenotypes of the rock rattlesnake (Crotalus lepidus) and the ridge-nosed rattlesnake (Crotalus willardi) from México and the United States. Toxicon 2017, 138, 119–129. [Google Scholar] [CrossRef] [PubMed]
  4. Perumal Samy, R.; Pachiappan, A.; Gopalakrishnakone, P.; Thwin, M.M.; Hian, Y.E.; Chow, V.T.; Bow, H.; Weng, J.T. In vitro antimicrobial activity of natural toxins and animal venoms tested against Burkholderia pseudomallei. BMC Infect. Dis. 2006, 6, 100. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  5. Ferreira, B.L.; Santos, D.O.; Dos Santos, A.L.; Rodrigues, C.R.; de Freitas, C.C.; Cabral, L.M.; Castro, H.C. Comparative analysis of Viperidae venoms antibacterial profile: A short communication for proteomics. Evid. Based Complement. Alternat. Med. 2001, 2011, 960267. [Google Scholar]
  6. Nevalainen, T.J.; Graham, G.G.; Scott, K.F. Antibacterial actions of secreted phospholipases A2. Biochim. Biophys. Acta 2008, 1781, 1–9. [Google Scholar] [CrossRef]
  7. Okubo, B.M.; Silva, O.N.; Migliolo, L.; Gomes, D.G.; Porto, W.F.; Batista, C.L.; Ramos, C.S.; Holanda, H.H.; Dias, S.C.; Franco, O.L.; et al. Evaluation of an antimicrobial L-amino acid oxidase and peptide derivatives from Bothropoides mattogrosensis pitviper venom. PLoS ONE 2012, 7, e33639. [Google Scholar] [CrossRef] [Green Version]
  8. De Barros, E.; Gonçalves, R.M.; Cardoso, M.H.; Santos, N.C.; Franco, O.L.; Cândido, E.S. Snake venom cathelicidins as natural antimicrobial peptides. Front. Pharmacol. 2019, 10, 1415. [Google Scholar] [CrossRef] [Green Version]
  9. Shinohara, L.; de Freitas, S.F.; da Silva, R.J.; Guimaraes, S. In vitro effects of Crotalus durissus terrificus and Bothrops jararaca venoms on Giardia duodenalis trophozoites. Parasitol. Res. 2006, 98, 339–344. [Google Scholar] [CrossRef]
  10. Adade, C.M.; Cons, B.L.; Melo, P.A.; Souto-Padron, T. Effect of Crotalus viridis viridis snake venom on the ultrastructure and intracellular survival of Trypanosoma cruzi. Parasitology 2011, 138, 46–58. [Google Scholar] [CrossRef]
  11. Bhattacharya, S.; Ghosh, P.; De, T.; Gomes, A.; Gomes, A.; Dungdung, S.R. In vivo and in vitro antileishmanial activity of Bungarus caeruleus snake venom through alteration of immunomodulatory activity. Experim. Parasitol. 2013, 135, 126–133. [Google Scholar] [CrossRef] [PubMed]
  12. Fallahi, N.; Shahbazzadeh, D.; Maleki, F.; Aghdasi, M.; Tabatabaie, F.; Khanaliha, K. The in vitro study of anti-leishmanial effect of Naja naja oxiana snake venom on Leishmania major. Infect. Disord. Drug Targets 2020, in press. [Google Scholar] [CrossRef] [PubMed]
  13. Martos Esteban, A.; Carrington, M.; Laustsen, A.H. Harnessing snake venoms to make T. brucei forever go to sleep. Toxicon 2018, 150, 320–321. [Google Scholar] [CrossRef]
  14. Allane, D.; Oussedik-Oumehdi, H.; Harrat, Z.; Seve, M.; Laraba-Djebari, F. Isolation and characterization of an anti-leishmanial disintegrin from Cerastes cerastes venom. J. Biochem. Mol. Toxicol. 2018, 32, e22018. [Google Scholar] [CrossRef]
  15. Dickerson, H.W.; Dawe, D.L. Ichthyophthirius multifiliis and Cryptocaryon irritans (phylum Ciliophora). In Fish Diseases and Disorders; Woo, P.T.K., Leatherland, J.F., Eds.; CAB International: Cambridge, MA, USA, 2006; pp. 116–153. [Google Scholar]
  16. Coyne, R.S.; Hannick, L.; Shanmugam, D.; Hostetler, J.B.; Brami, D.; Joardar, V.S.; Johnson, J.; Radune, D.; Singh, I.; Badger, J.H.; et al. Comparative genomics of the pathogenic ciliate Ichthyophthirius multifiliis, its free-living relatives and a host species provide insights into adoption of a parasitic lifestyle and prospects for disease control. Genome Biol. 2011, 12, R100. [Google Scholar] [CrossRef] [Green Version]
  17. Sharon, G.; Leibowitz, M.P.; Chettri, J.K.; Isakov, N.; Zilberg, D.J. Disease in wildlife or exotic species. Comparative study of infection with Tetrahymena of different ornamental fish species. Comp. Path. 2014, 150, 316–324. [Google Scholar] [CrossRef]
  18. Astrofsky, K.M.; Schech, J.M.; Sheppard, B.J.; Obenschain, C.A.; Chin, A.M.; Kacergis, M.C.; Laver, E.R.; Bartholomew, J.L.; Fox, J.G. High mortality due to Tetrahymena sp. infection in laboratory-maintained zebrafish (Brachydanio rerio). Comp. Med. 2002, 52, 363–367. [Google Scholar]
  19. Sauvant, M.; Pepin, D.; Piccinni, E. Tetrahymena pyriformis: A tool for toxicological studies: A review. Chemosphere 1999, 38, 1631–1669. [Google Scholar] [CrossRef]
  20. Zilberg, D.; Sinai, T. Optimization and validation of a colorimetric assay for Tetrahymena sp. survival. Res. Microbiol. 2006, 157, 355–359. [Google Scholar] [CrossRef]
  21. Kuleshina, O.N.; Kozlov, L.V.; Cheremnykh, E.G. A universal method for measuring functional activity of complement in humans, laboratory, domestic, and agricultural animals, amphibians, and birds. Bull. Exp. Biol. Med. 2014, 157, 285–287. [Google Scholar] [CrossRef]
  22. Nunes, D.C.; Figueira, M.M.; Lopes, D.S.; De Souza, D.L.; Izidoro, L.F.; Ferro, E.A.; Souza, M.A.; Rodrigues, R.S.; Rodrigues, V.M.; Yoneyama, K.A. BnSP-7 toxin, a basic phospholipase A2 from Bothrops pauloensis snake venom, interferes with proliferation, ultrastructure and infectivity of Leishmania (Leishmania) amazonensis. Parasitology 2013, 140, 844–854. [Google Scholar] [CrossRef] [PubMed]
  23. Bastos, L.M.; Junior, R.J.; Silva, D.A.; Mineo, J.R.; Vieira, C.U.; Teixeira, D.N.; Homsi-Brandeburgo, M.I.; Rodrigues, V.M.; Hamaguchi, A. Toxoplasma gondii: Effects of neuwiedase, a metalloproteinase from Bothrops neuwiedi snake venom, on the invasion and replication of human fibroblasts in vitro. Exp. Parasitol. 2008, 120, 391–396. [Google Scholar] [CrossRef]
  24. Tempone, A.G.; Andrade, H.F., Jr.; Spencer, P.J.; Lourenco, C.O.; Rogero, J.R.; Nascimento, N. Bothrops moojeni venom kills Leishmania spp. with hydrogen peroxide generated by its L-amino acid oxidase. Biochem. Bioph. Res. Commun. 2001, 280, 620–624. [Google Scholar] [CrossRef] [PubMed]
  25. Fernandez-Gomez, R.; Zerrouk, H.; Sebti, F.; Loyens, M.; Benslimane, A.; Ouaissi, M.A. Growth inhibition of Trypanosoma cruzi and Leishmania donovani infantum by different snake venoms: Preliminary identification of proteins from Cerastes cerastes venom which interact with the parasites. Toxicon 1994, 32, 875–882. [Google Scholar] [CrossRef]
  26. Yap, M.K.; Fung, S.Y.; Tan, K.Y.; Tan, N.H. Proteomic characterization of venom of the medically important Southeast Asian Naja sumatrana (Equatorial spitting cobra). Acta Trop. 2014, 133, 15–25. [Google Scholar]
  27. Chong, H.P.; Tan, K.Y.; Tan, N.H.; Tan, C.H. Exploring the diversity and novelty of toxin genes in Naja sumatrana, the equatorial spitting cobra from Malaysia through de novo venom-gland transcriptomics. Toxins (Basel) 2019, 11, 104. [Google Scholar] [CrossRef] [Green Version]
  28. Dubovskii, P.V.; Lesovoy, D.M.; Dubinnyi, M.A.; Konshina, A.G.; Utkin, Y.N.; Efremov, R.G.; Arseniev, A.S. Interaction of three-finger toxins with phospholipid membranes: Comparison of S- and P-type cytotoxins. Biochem. J. 2005, 387, 807–815. [Google Scholar] [CrossRef]
  29. Feofanov, A.V.; Sharonov, G.V.; Dubinnyi, M.A.; Astapova, M.V.; Kudelina, I.A.; Dubovskii, P.V.; Rodionov, D.I.; Utkin, Y.N.; Arseniev, A.S. Comparative study of structure and activity of cytotoxins from venom of the cobras Naja oxiana, Naja kaouthia, and Naja haje. Biochemistry (Moscow) 2004, 69, 1148–1157. [Google Scholar] [CrossRef]
  30. Osipov, A.V.; Astapova, M.V.; Tsetlin, V.I.; Utkin, Y.N. The first representative of glycosylated three-fingered toxins. Cytotoxin from the Naja kaouthia cobra venom. Eur. J. Biochem. 2004, 271, 2018–2027. [Google Scholar] [CrossRef]
  31. Chien, K.Y.; Chiang, C.M.; Hseu, Y.C.; Vyas, A.A.; Rule, G.S.; Wu, W. Two distinct types of cardiotoxin as revealed by the structure and activity relationship of their interaction with zwitterionic phospholipid dispersions. J. Biol. Chem. 1994, 269, 14473–14483. [Google Scholar] [PubMed]
  32. Gasanov, S.E.; Shrivastava, I.H.; Israilov, F.S.; Kim, A.A.; Rylova, K.A.; Zhang, B.; Dagda, R.K. Naja naja oxiana Cobra Venom Cytotoxins CTI and CTII Disrupt Mitochondrial Membrane Integrity: Implications for Basic Three-Fingered Cytotoxins. PLoS ONE 2015, 10, e0129248. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  33. Primor, N.; Sabnay, I.; Lave, V.; Zlotkin, E. Toxicity to fish, effect on gill ATPase and gill ultrastructural changes induced by Pardachirus secretion and its derived toxin pardaxin. J. Exptl. Zool. 1980, 211, 33–43. [Google Scholar] [CrossRef]
  34. Feofanov, A.V.; Sharonov, G.V.; Astapova, M.V.; Rodionov, D.I.; Utkin, Y.N.; Arseniev, A.S. Cancer cell injury by cytotoxins from cobra venom is mediated through lysosomal damage. Biochem. J. 2005, 390, 11–18. [Google Scholar] [CrossRef] [PubMed]
  35. Ramazanova, A.S.; Zavada, L.L.; Starkov, V.G.; Kovyazina, I.V.; Subbotina, T.F.; Kostyukhina, E.E.; Dementieva, I.N.; Ovchinnikova, T.V.; Utkin, Y.N. Heterodimeric neurotoxic phospholipases A2—The first proteins from venom of recently established species Vipera nikolskii: Implication of venom composition in viper systematics. Toxicon 2008, 51, 524–537. [Google Scholar] [CrossRef] [PubMed]
  36. Tran, T.V.; Siniavin, A.E.; Hoang, A.N.; Le, M.T.T.; Pham, C.D.; Phung, T.V.; Nguyen, K.C.; Ziganshin, R.H.; Tsetlin, V.I.; Weng, C.F.; et al. Phospholipase A2 from krait Bungarus fasciatus venom induces human cancer cell death in vitro. PeerJ 2019, 7, e8055. [Google Scholar] [CrossRef] [Green Version]
  37. Tsai, I.H.; Wang, Y.M.; Cheng, A.C.; Starkov, V.; Osipov, A.; Nikitin, I.; Makarova, Y.; Ziganshin, R.; Utkin, Y. cDNA cloning, structural, and functional analyses of venom phospholipases A2 and a Kunitz-type protease inhibitor from steppe viper Vipera ursinii renardi. Toxicon 2011, 57, 332–341. [Google Scholar] [CrossRef]
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Figure 1. Anti-protozoan activity of cobra venoms. Indicated volume of cobra venom solution in water (50 mg/mL) was added to the instrument well containing 300 μL of infusoria suspension comprising about 800–1000 microorganisms and the number of moving (survived) organisms was counted over the time using the BioLaT-3.2 instrument.
Figure 1. Anti-protozoan activity of cobra venoms. Indicated volume of cobra venom solution in water (50 mg/mL) was added to the instrument well containing 300 μL of infusoria suspension comprising about 800–1000 microorganisms and the number of moving (survived) organisms was counted over the time using the BioLaT-3.2 instrument.
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Figure 2. Separation of cobra Naja sumatrana venom by gel-filtration (A), ion-exchange (B) and reversed phase chromatography (C,D). A. Gel-filtration was performed using SuperdexTM 75 column equilibrated with 0.1 M ammonium acetate buffer (pH 6.2) at flow rate of 0.5 mL/min. The collected fractions are underlined. B. The toxic faction IV (Figure 2A) was separated on a HEMA BIO 1000 CM column (8 × 250 mm, Tessek, Prague, Czech Republic) applying a gradient of 5–700 mM ammonium acetate (pH 7.5) in 140 min, at a flow rate of 0.5 mL/min. Fractions obtained (Figure 2B) were screened for lethal activity and toxic fractions 10 and 11 were further separated on a Bio Wide Pore C18 column (10 × 250 mm) in a gradient of acetonitrile 20–50% in 60 min in the presence of 0.1% trifluoroacetic acid, at a flow rate of 2.0 mL/min. C – separation of fraction 10 (Figure 2B); D – separation of fraction 11 (Figure 2B). In panels B, C and D, the fractions toxic to infusorians are indicated by horizontal bars.
Figure 2. Separation of cobra Naja sumatrana venom by gel-filtration (A), ion-exchange (B) and reversed phase chromatography (C,D). A. Gel-filtration was performed using SuperdexTM 75 column equilibrated with 0.1 M ammonium acetate buffer (pH 6.2) at flow rate of 0.5 mL/min. The collected fractions are underlined. B. The toxic faction IV (Figure 2A) was separated on a HEMA BIO 1000 CM column (8 × 250 mm, Tessek, Prague, Czech Republic) applying a gradient of 5–700 mM ammonium acetate (pH 7.5) in 140 min, at a flow rate of 0.5 mL/min. Fractions obtained (Figure 2B) were screened for lethal activity and toxic fractions 10 and 11 were further separated on a Bio Wide Pore C18 column (10 × 250 mm) in a gradient of acetonitrile 20–50% in 60 min in the presence of 0.1% trifluoroacetic acid, at a flow rate of 2.0 mL/min. C – separation of fraction 10 (Figure 2B); D – separation of fraction 11 (Figure 2B). In panels B, C and D, the fractions toxic to infusorians are indicated by horizontal bars.
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Figure 3. Influence of fractions obtained during separation of N. sumatrana venom on survival of T. pyriformis. (A,B) – fractions obtained after gel-filtration and numbered according to Figure 2A.; (C) – fractions obtained after ion-exchange chromatography and numbered according to Figure 2B. One fourth of each fraction was freeze-dried and dissolved in 100 μL of water. Each toxin solution was added to 300 μL of infusorian suspension and the number of moving (survived) microorganisms was counted using BioLaT-3.2 instrument. The volume added is indicated in brackets.
Figure 3. Influence of fractions obtained during separation of N. sumatrana venom on survival of T. pyriformis. (A,B) – fractions obtained after gel-filtration and numbered according to Figure 2A.; (C) – fractions obtained after ion-exchange chromatography and numbered according to Figure 2B. One fourth of each fraction was freeze-dried and dissolved in 100 μL of water. Each toxin solution was added to 300 μL of infusorian suspension and the number of moving (survived) microorganisms was counted using BioLaT-3.2 instrument. The volume added is indicated in brackets.
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Figure 4. The toxicity of cytotoxins from N. sumatrana (NS) and N. oxiana (CX1 and CX2) venoms to T. pyriformis. Fractions and toxins were dissolved in water at the concentration of 20 mg/mL. 10 μL of each toxin solution was added to 200 μL of infusorian suspension (about 800 microorganisms) and the number of survived microorganisms was counted using the BioLaT-3.2 instrument. Final toxin concentration was 0.95 mg/mL. (A) NSIV-10 and NSIV-11 – fractions 10 and 11 from Figure 2B, respectively; CX1 and CX2 – cytotoxins 1 and 2 from N. oxiana. (B) NSIV-10-1 – fraction 1 from Figure 2C. NSIV-11-1, NSIV-11-2 and NSIV-11-3 – fractions 1, 2 and 3 from Figure 2D, respectively.
Figure 4. The toxicity of cytotoxins from N. sumatrana (NS) and N. oxiana (CX1 and CX2) venoms to T. pyriformis. Fractions and toxins were dissolved in water at the concentration of 20 mg/mL. 10 μL of each toxin solution was added to 200 μL of infusorian suspension (about 800 microorganisms) and the number of survived microorganisms was counted using the BioLaT-3.2 instrument. Final toxin concentration was 0.95 mg/mL. (A) NSIV-10 and NSIV-11 – fractions 10 and 11 from Figure 2B, respectively; CX1 and CX2 – cytotoxins 1 and 2 from N. oxiana. (B) NSIV-10-1 – fraction 1 from Figure 2C. NSIV-11-1, NSIV-11-2 and NSIV-11-3 – fractions 1, 2 and 3 from Figure 2D, respectively.
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Figure 5. Amino acid sequences of cobra cytotoxins. Fragment 45–50 not identified by MALDI mass spectrometry in NSIV-10-1 is underlined. Nsp – N. sputatrix, No- N. oxiana, Nk – N. kaouthia.
Figure 5. Amino acid sequences of cobra cytotoxins. Fragment 45–50 not identified by MALDI mass spectrometry in NSIV-10-1 is underlined. Nsp – N. sputatrix, No- N. oxiana, Nk – N. kaouthia.
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Figure 6. The toxicity of cytotoxin 3 (CX3) and glycosylated cytotoxin 3 (GCX) from N. kaouthia venom to T. pyriformis. The conditions for activity measurements were the same as in Figure 4.
Figure 6. The toxicity of cytotoxin 3 (CX3) and glycosylated cytotoxin 3 (GCX) from N. kaouthia venom to T. pyriformis. The conditions for activity measurements were the same as in Figure 4.
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Figure 7. Microscopic images of cytotoxin-treated T. pyriformis. (A) Normal teardrop-like shaped T. pyriformis cells (control) were treated with cytotoxin 2 (1 mg/mL) during the time indicated. The cellular shape became spherical during the treatment and the leakage of cell content became evident as indicated by arrow. (B) T. pyriformis cells were incubated with fluorescently labeled cytotoxin 2 (1 mg/mL) during the time indicated. The photographs were taken in light transmission mode (light) and fluorescence mode (fluorescence).
Figure 7. Microscopic images of cytotoxin-treated T. pyriformis. (A) Normal teardrop-like shaped T. pyriformis cells (control) were treated with cytotoxin 2 (1 mg/mL) during the time indicated. The cellular shape became spherical during the treatment and the leakage of cell content became evident as indicated by arrow. (B) T. pyriformis cells were incubated with fluorescently labeled cytotoxin 2 (1 mg/mL) during the time indicated. The photographs were taken in light transmission mode (light) and fluorescence mode (fluorescence).
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Table
Table 1. Death times of 50% of the ciliates in the presence of cobra venoms.
Table 1. Death times of 50% of the ciliates in the presence of cobra venoms.
SpeciesVenom Concentration, mg/mLTime to Death 50% of Ciliates, min
N. nigricollis0.331.75
N. sumatrana0.332.5
N. naja0.336.6
N. kaouthia0.3314.0
N. oxiana1.612.5
N. nivea1.619.6
N. melanoleuca1.6118.0
Table
Table 2. Death time of 50% of ciliates in the presence of cobra cytotoxins. Toxin concentration is 0.95 mg/mL.
Table 2. Death time of 50% of ciliates in the presence of cobra cytotoxins. Toxin concentration is 0.95 mg/mL.
ToxinToxin TypeTime to Death 50% of Ciliates, min
CX2 N. oxianaP-type1.5
NSIV-11-3P-type2.0
CX3 N. kaouthiaS-type2.3
CX1 N. oxianaS-type5.4
NSIV-10-1S-type17.5
NSIV-11-1n.d.8.5
NSIV-11-2n.d.5.8
Table
Table 3. Comparison of theoretical digestion fragments of cytotoxin 2c and cardiotoxin 5A N. sputatrix with those found in tryptic digests of proteins Ns4-10-1 and Ns4-11-1 from N. sumatrana.
Table 3. Comparison of theoretical digestion fragments of cytotoxin 2c and cardiotoxin 5A N. sputatrix with those found in tryptic digests of proteins Ns4-10-1 and Ns4-11-1 from N. sumatrana.
Molecular Masses, DaPosition in the SequenceAmino Acid Sequence
DeterminedCalculated
NsIV-10-1NsIV-11-1Cytotoxin
2C		Cardiotoxin
5A
576.15576.13576.2813–18TCPAGK
No signal598.25598.40 32–36VPVKR
605.22605.20605.341–5LKCNK
640.18640.16640.3219–23NLCYK
No signal646.26646.41 45–50SSLLVK
834.27834.22834.3837–44GCIDVCPK
879.43879.38879.536–12LVPLFYK
No signal940.30940.46 24–31MYMVATPK
973.25973.23973.3951–58YVCCNDTR
1190.271190.231190.4451–60YVCCNDTRCN
1365.57No signal 1365.7324–35MFMVSNLTVPVK
1521.65No signal 1521.8324–36MFMVSNLTVPVKR

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Kuleshina, O.N.; Kruykova, E.V.; Cheremnykh, E.G.; Kozlov, L.V.; Andreeva, T.V.; Starkov, V.G.; Osipov, A.V.; Ziganshin, R.H.; Tsetlin, V.I.; Utkin, Y.N. Screening Snake Venoms for Toxicity to Tetrahymena Pyriformis Revealed Anti-Protozoan Activity of Cobra Cytotoxins. Toxins 2020, 12, 325. https://doi.org/10.3390/toxins12050325

AMA Style

Kuleshina ON, Kruykova EV, Cheremnykh EG, Kozlov LV, Andreeva TV, Starkov VG, Osipov AV, Ziganshin RH, Tsetlin VI, Utkin YN. Screening Snake Venoms for Toxicity to Tetrahymena Pyriformis Revealed Anti-Protozoan Activity of Cobra Cytotoxins. Toxins. 2020; 12(5):325. https://doi.org/10.3390/toxins12050325

Chicago/Turabian Style

Kuleshina, Olga N., Elena V. Kruykova, Elena G. Cheremnykh, Leonid V. Kozlov, Tatyana V. Andreeva, Vladislav G. Starkov, Alexey V. Osipov, Rustam H. Ziganshin, Victor I. Tsetlin, and Yuri N. Utkin. 2020. "Screening Snake Venoms for Toxicity to Tetrahymena Pyriformis Revealed Anti-Protozoan Activity of Cobra Cytotoxins" Toxins 12, no. 5: 325. https://doi.org/10.3390/toxins12050325

APA Style

Kuleshina, O. N., Kruykova, E. V., Cheremnykh, E. G., Kozlov, L. V., Andreeva, T. V., Starkov, V. G., Osipov, A. V., Ziganshin, R. H., Tsetlin, V. I., & Utkin, Y. N. (2020). Screening Snake Venoms for Toxicity to Tetrahymena Pyriformis Revealed Anti-Protozoan Activity of Cobra Cytotoxins. Toxins, 12(5), 325. https://doi.org/10.3390/toxins12050325

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