Rattlesnake Crotalus molossus nigrescens venom induces oxidative stress on human erythrocytes
© The Author(s). 2017
Received: 5 November 2016
Accepted: 12 April 2017
Published: 21 April 2017
Globally, snake envenomation is a well-known cause of death and morbidity. In many cases of snakebite, myonecrosis, dermonecrosis, hemorrhage and neurotoxicity are present. Some of these symptoms may be provoked by the envenomation itself, but others are secondary effects of the produced oxidative stress that enhances the damage produced by the venom toxins. The only oxidative stress effect known in blood is the change in oxidation number of Fe (from ferrous to ferric) in hemoglobin, generating methemoglobin but not in other macromolecules. Currently, the effects of the overproduction of methemoglobin derived from snake venom are not extensively recorded. Therefore, the present study aims to describe the oxidative stress induced by Crotalus molossus nigrescens venom using erythrocytes.
Human erythrocytes were washed and incubated with different Crotalus molossus nigrescens venom concentrations (0–640 μg/mL). After 24 h, the hemolytic activity was measured followed by attenuated total reflectance-Fourier transform infrared spectroscopy, non-denaturing PAGE, conjugated diene and thiobarbituric acid reactive substances determination.
Low concentrations of venom (<10 μg/mL) generates oxyhemoglobin release by hemolysis, whereas higher concentrations produced a hemoglobin shift of valence, producing methemoglobin (>40 μg/mL). This substance is not degraded by proteases present in the venom. By infrared spectroscopy, starting in 80 μg/mL, we observed changes in bands that are associated with protein damage (1660 and 1540 cm−1) and lipid peroxidation (2960, 2920 and 1740 cm−1). Lipid peroxidation was confirmed by conjugated diene and thiobarbituric acid reactive substance determination, in which differences were observed between the control and erythrocytes treated with venom.
Crotalus molossus nigrescens venom provokes hemolysis and oxidative stress, which induces methemoglobin formation, loss of protein structure and lipid peroxidation.
KeywordsAttenuated total reflectance-Fourier transform infrared spectroscopy Crotalus molossus nigrescens Venom Snake venom Methemoglobin Oxidative stress Oxyhemoglobin
Snakebites cause considerable death and high morbidity worldwide and pose an important threat to public health, especially those provoked by Crotalus snakes [1–4]. Rattlesnake envenomation alters the homeostasis of victims, generating coagulation alterations and hemorrhage that may provoke death. Rattlesnake envenomation may cause myonecrosis, dermonecrosis, neurotixicity, different types of damage to the vascular extracellular matrix, and edema . These effects are generated by some toxins such as phospholipases A2 (PLA2), low molecular mass myotoxins, L-amino acid oxidases (LAAO) and proteases including metalloproteinases (SVMPs) and serineproteinases (SVSPs) [6–8]. In addition, reactive oxygen species (ROS) are produced as a side effect of the catalytic activity of some toxins, enhancing the damage produced by the venom and causing systemic oxidative stress .
The different scenarios on the oxidative stress indicate that are unrecognized and underestimated forms of affliction provoked by snakes. SVMPs, major components in most Crotalid venoms, have a relevant role in venom-induced local damage. The lethality of this venom is due to the high activity of PLA2 that hydrolyzes phospholipids and releases arachidonic acid, which, in turn, generates toxic reactive oxygen species (ROS) [10, 11]. This reaction results in lipid peroxidation and leads to cellular damage .
Cells have antioxidant defenses against toxic ROS – such as the enzymes superoxide dismutase (SOD) and catalase (CAT) – that work in tandem to neutralize superoxide radicals [13–15]. SOD catalyzes the loss of superoxide radicals into oxygen or hydrogen peroxide (H2O2); this is itself detrimental and must be detoxified into other non-toxic substances. By another way, CAT helps in the decomposition of H2O2 into water and oxygen . All these responses are part of the reactions triggered by C. m. nigrescens venom (CMNv), which produce significant oxidative stress in different stages. Thus, an important role of lipid peroxidation in cytotoxicity of C. m. nigrescens envenomation is suggested. Based on these relevant findings of oxidative stress produced by snakebite, the present study aims to describe the oxidative stress induced by CMNv using a model of isolated erythrocytes.
Venom samples were obtained from C. m. nigrescens specimens maintained at the Universidad Autónoma de Queretaro herpetarium. Venom extraction was performed manually as described by Meléndez-Martínez et al. . CMNv was pooled, lyophilized and stored at −20 °C until use. Protein concentration in venom was measured by Lowry protein assay , using bovine serum albumin as standard.
Hemolytic activity was determined using Das et al.  protocol with some modifications. Blood was collected from at least three healthy donors for each experiment. Inclusion criteria were: O+ donors that had not taken any medication 48 h before the test. Blood samples were collected in BD Vacutainer® buffered sodium citrate tubes and erythrocytes were isolated and washed thrice by centrifugation at 1,100 g and re-suspended in 0.9% saline solution to a final concentration of 20%. Then, 37.5 μL of erythrocyte suspension was incubated during 24 h at 37 °C with different CMNv concentrations (0–640 μg/mL) in a 500 μL final volume. Next, the samples were centrifuged at 6,400 g for 10 min and supernatant was measured at 540 nm for oxyhemoglobin (Oxy-Hb) and 630 nm for methemoglobin (Met-Hb) in a Helios Omega UV–vis spectrophotometer (Thermo Scientific, USA). As 100% Oxy-Hb and Met-Hb controls distilled H2O and H2O2 5% (v/v) were used, respectively.
Polyacrylamide gel electrophoresis
These experiments were carried out under non-denaturing and denaturing polyacrylamide gel electrophoresis (PAGE) using a 15% acrylamide gel modified from Sambrook and Russell  to observe the degradation of the hemoglobin (Hb). Treated erythrocytes were centrifuged as described above and 50 μg of soluble Hb was collected to use in the gels and stained 0.1% Coomassie blue R-250 staining. The samples used in denaturing PAGE were sand boiled by 5 min before the electrophoresis.
Attenuated total reflectance-Fourier transform infrared spectroscopy
Erythrocytes were treated as described in hemolysis assay. The CMNv treated erythrocytes were analyzed in attenuated total reflectance-Fourier transform infrared (ATR-FTIR) in a Bruker Alpha FTIR Spectrometer (Bruker Optics, USA), according to the method described in Barraza-Garza et al. . Briefly, 4 μL of treated erythrocytes were placed at the spectrometer and were allowed to dry for 10 min. Spectra were recorded in a range from 4000 to 900 cm−1 with a maximum resolution of 6 cm−1, and 200 scans per spectrum were collected. Three spectra were recorded for each treatment.
Infrared spectra analysis
Infrared (IR) spectra were analyzed using Unscrambler® X software (CAMO Software, Norway). Raw spectra were preprocessed using first vector normalization and then a second derivative using Savitsky-Golay of second polynomial order with 21 smoothing points. The second derivative spectra obtained was analyzed in order to observe differences in intensity and position of the signals. The analysis was made in three main zones across the spectra that are related to chemical bonds liable to damage via oxidative stress : ~1550-1660 cm−1 region for amide I and II, ~1740-1780 cm−1 region for aldehyde bond and ~2920-2960 cm−1 region for primary and secondary carbon bonds in lipid skeletons.
Conjugated dienes determination
Conjugated dienes (CD) were determined according to Barraza-Garza et al.  with slight modifications. After treatment, the erythrocytes were resuspended in 900 μL of methanol:chloroform (1:2) solution and vortexed for 2 min. The mixture was centrifuged for 10 min at 4650 g and the chloroform phase was collected and dried with a nitrogen flux. Then, lipids were dissolved in 200 μL of cyclohexane, mixed by vortex for 30 s and immediately measured at 233 nm in a Helios Omega UV–vis spectrophotometer (Thermo Scientific, USA) using cyclohexane as blank. Absorbance was converted to conjugated dienes concentration using an extinction coefficient of 27000 M−1cm−1 and the results were expressed as concentration (μM) of conjugated dienes per sample.
Thiobarbituric acid reactive substances assay
Thiobarbituric acid reactive substances assay (TBARS) was performed according to Barraza-Garza et al.  with slight modifications. After treatment, 100 μL of venom-treated erythrocytes were mixed with 400 μL of thiobarbituric acid reagent (20% trichloroacetic acid; 0.5% thiobarbituric acid and 2.5 N HCl) and the mixture was heated for 1 h at 75 °C. After cooling, the solution was centrifuged at 380 g for 10 min and the absorbance of supernatant was measured at 532 nm in a Helios Omega UV–vis spectrophotometer (Thermo Scientific, USA) using the reaction mixture as a blank. Results were expressed as concentration (μM) of malondialdehyde (MDA) per sample. A calibration curve was prepared with tetramethoxypropane (which is equivalent to the same concentrations of MDA) with concentrations ranging from 1.25 to 20 μM.
Results obtained with CD and TBARS were analyzed by a one-way analysis of variance (ANOVA). When ANOVA showed a significant difference, Tukey’s post hoc test was applied. Multivariate analysis was made by PCA as described in the previous subsection, using Unscrambler® X software (CAMO Software, Norway).
Results and discussion
Hemolysis could be produced as consequence of PLA2 phospholipid degradation and L-amino acid oxidase catalysis [22, 23]. Due to Oxy-Hb release, the ferrous (Fe2+) heme was converted to ferric (Fe3+) heme resulting in Met-Hb. This valence shift in Hb could be generated by oxidative stress induced by H2O2 produced by the LAAO catalysis [24, 25]. Then, Hb damage could be magnified by the Met-Hb formation itself, acting as a prooxidant molecule accelerating de process of Met-Hb formation .
Oxidative stress evaluation by attenuated total reflectance-Fourier transform infrared spectroscopy
Infrared spectroscopy allowed us to observe differences of the different biomolecules on erythrocytes due to oxidative stress by CMNv concentration increase. ATR-FTIR analysis was carried out at the regions associated to lipid (2960, 2920 and 1740 cm−1) and protein oxidation (1660 and 1540 cm−1) bands to determine the oxidation in proteins. No differences were observed between control samples and those treated with a low venom concentration (10–40 μg/mL).
Changes in both amide I and II can be seen at venom concentrations higher than 80 μg/mL. In Fig. 3c it is possible to observe a loss of symmetry of the peak and a displacement to higher wave number, and a decrease of intensity of both bands as the concentration of venom increases. This decrease in the intensity of the bands can be associated with changes in the secondary and tertiary structure from proteins, mainly Hb, related to the loss of integrity of proteins caused by the oxidative stress .
Spectrophotometric measures of lipid peroxidation by conjugated dienes and thiobarbituric acid reactive substances assay
a change in the proportion of primary and secondary carbons of the lipid skeleton related to structure loss in lipids by lipid peroxidation;
an intensity increase of the aldehyde band related to the production of secondary products of the lipid peroxidation.
TBARS assay validated the effects observed in the ATR-FTIR assay for aldehyde band (Fig. 4b) as well as for CD. Through TBARS assay, it was possible to observe an increase of MDA as the concentration of venom augmented. However, this increase was only significant for the highest venom concentration. Considering that TBARS represent the formation of secondary products of lipid peroxidation, this results may suggest that at the time and concentration studied, the venom produced mainly primary products of lipid oxidation. Interestingly, both Oxy-Hb and Met-Hb treatments had a lower concentration of MDA than that seen in the control treatment (0 μg/mL), suggesting that the catalytic activity of the venom is involved in the production of aldehyde compounds and not as an oxidative effect of Met-Hb.
This increment of MDA could be produced due the arachidonic acid release after PLA2 catalysis . Moreover, the newly produced arachidonic acid could be oxidized by H2O2 produced by the LAAO catalysis . Al Asmari et al.  reported an increment of MDA levels in the liver, kidney, heart, and brain of mice treated with Echis pyramidum venom. Similarly to our results, they reported a MDA increase after 24 h of incubation, suggesting that the oxidative stress produced by the CMNv in the erythrocytes can lead to a systemic lipid peroxidation affecting other tissues.
In conclusion, through ATR-FTIR, CD, and TBARS we demonstrate that the venom of Crotalus molossus nigrescens is an oxidative stress inductor generating Met-Hb, loss of protein structure and lipid peroxidation in erythrocytes, which can be related to some of the symptoms observed in the envenomation.
One-way analysis of variance
Attenuated total reflectance-Fourier transform infrared
Crotalus molossus nigrescens venom
- H2O2 :
L-amino acid oxidases
Polyacrylamide gel electrophopresis
- PLA2 :
Reactive oxygen species
Snake Venom Metalloproteinases
Snake Venom Serineproteinases
Thiobarbituric acid reactive substances assay
Special acknowledgements to Dr. Simón Yobanny Reyes-López from Laboratorio de Materiales Híbridos Nanoestructurados from Universidad Autónoma de Ciudad Juárez for allowing us to use the ATR-FTIR spectrometer.
This project was supported by Programa Integral de Fortalecimiento Institucional, SEP (PIFI) for Academic Groups, Universidad Autónoma de Ciudad Juárez.
Availability of data and materials
DMM and GBG performed the experiments; MSCP contributed with the C. m. nigrescens venom used in this research; DMM, GBG, JMM, AGC, EAP and LFPT analyzed the data and wrote the paper. All the authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Consent for publication
Ethics approval and consent to participate
The C. m. nigrescens specimens used were maintained in captivity under permit of the Direccion General de Vida Silvestre of Secretaria de Medio Amiente y Recursos Naturales de México (INE/CITES/DGVS-CR-IN-0619-QRO-00) at the Universidad Autónoma de Queretaro.
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