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Anti-inflammatory effects of Neurotoxin-Nna, a peptide separated from the venom of Naja naja atra
© Ruan et al.; licensee BioMed Central Ltd. 2013
Received: 25 November 2012
Accepted: 11 March 2013
Published: 15 April 2013
Neurotoxin-Nna (NT), an analgesic peptide separated from the venom of Naja naja atra, has reported to have an exceptional specificity to block transmission of the nerve impulse by binding to the α- subunit of the nicotinic acetylcholine receptor in the membrane. However, little information is available on the anti-inflammatory effects of NT. Therefore, the anti-inflammatory activity of Neurotoxin-Nna was investigated in this study.
The anti-inflammatory effects of NT were evaluated by measuring its influence on several crucial factors in inflammatory pathways, including total antioxidant activity, antinociceptive effects in vivo, nuclear factor kappa B (NF-κB), polymorphonuclear cells (PMN), inducible nitric oxide synthase (iNOS), adhesion molecule (ICAM-1) and tactile hyperalgesia.
NT treatment decreased the levels of tumor necrosis factor alpha (TNF-α) and interleukin 1 beta (IL-1β). NT treatment decreased the total antioxidant status (TAOS) and reduced CFA-induced tactile hyperalgesia in a dose-dependent manner. NT significantly inhibited regulation of NF-kappaB activation and the production of IL-1β, TNF-α, iNOS and CAM-1. Moreover, NT suppressed infiltration of PMN.
Our results showed that NT reduced CFA-induced tactile hyperalgesia through inhibition inflammatory pathways in experimental inflammatory rats.
Snake venoms are composed mainly of proteins and peptides, which possess a variety of biological activities. Most of snake venoms have demonstrated antinociceptive activity, and certain isolated neurotoxins have demonstrated significant analgesia in animal models [1, 2]. Neurotoxin-Nna (NT), an analgesic peptide separated from the venom of Naja naja atra [3, 4], is endowed an exceptional specificity of action that block transmission of the nerve impulse by binding to the α- subunit of the nicotinic acetylcholine receptor in the membrane [5–7].
Pain is often associated with inflammation, which results from tissue damage, chemical stimuli or autoimmune processes. These stimuli induce the release of inflammatory mediators (prostaglandins, bradykinin, histamine, growth-factors and neurogenic factors) . These processes can lead to central sensitization and hypersensitivity. The antinociceptive effects of neurotoxins from snake venoms of Naja naja atra have been reported [1, 2]. NT, one of the main components in the venom of Naja naja atra, produced significantly analgesic effects in animal model. However, there is little information available about the anti-inflammatory effects of NT. We undertook the present study to ascertain whether NT has the anti-inflammatory effects in rats.
Healthy male Wistar rats (2 months old and weighing 225 ± 25 g) and female Kunming strain mice (weighing 20-22 g) were purchased from the Experimental Animal Center of Zhejiang Chinese Medical University. The study was approved by Zhejiang University’s ethics committee, and all animal experiments followed the Guidelines published by the Ministry of Science and Technology of the People's Republic of China. Care was taken to minimize discomfort, distress, and pain to the animals.
Anti-hyperalgesia effect of NT in mice
Ten mice received a single intraplantar injection of 100 μl of 1 mg/ml dose of heat-killed and dried Mycobacterium tuberculosis in a mixture of paraffin oil and mannide monoleate. The tactile hyperalgesia was tested as tactile withdrawal threshold before and 15, 30 and 60 min after drug administration.
Anti -inflammatory effects in rats
Thirty-six rats were randomly divided into six groups: (1) animals were treated only with intrapleural injection (i.p.) of sterile saline (NaCl 0.95%) (Control group), (2) animals were treated with carrageenan (i.p.) and orally administrated with saline 10 ml/kg (Inflammatory group), (3) animals were treated with carrageenan (i.p.) and orally administrated with diclofanac 1.7 mg/kg (Diclofanac group), (4) animals were treated with carrageenan (i.p.) and orally administrated with NT 1.0 mg/kg (NT-1 group), (5) animals were treated with carrageenan (i.p.) and orally administrated with NT 2.0 mg/kg (NT −2 group) and (6) animals were treated with carrageenan (i.p.) and orally administrated with NT 4.0 mg/kg (NT-4 group). The NT (1.0, 2.0 or 4.0 mg/ kg body wt.), diclofanac sodium (1.7 mg/kg) and vehicle (saline 10 ml/kg) were administrated with respective drugs 1 h before the injection of carrageenan. Inflammatory was induced by a single intrapleural injection of 0.1 mL of sterile saline (NaCl, 0.95%) plus carrageenan (Cg, 1%). Six hours after the injection of carrageenan, blood samples were collected from orbital vein in all rats and serum was separated for biochemical estimations.
Measurement of IL-1β, TNF-α level and activation of NF-κB
The serum concentration of tumor necrosis factor alpha (TNF-α) and interleukin 1 beta (IL-1β) were measured using a commercial enzyme-linked immunosorbent assay (ELISA) kit (Shanghai Jinma Biological Technology, Inc., China) following the manufacture’s instruction. Activated Nuclear factor kappa B (NF-κB) was tested via ELISA-technique using the PathScan Phospho-NFκB p65 (Ser536) Sandwich ELISA Antibody Pair (Shanghai Yubo Biological Technology, Inc., China), following the manufacture’s instruction. Briefly, the activated NF-κB specifically binds to oligonucleotides corresponding to NF-κB consensus binding sites and immobilized in a 96-well plate. Bound NF-κB is detected with an anti-p65 antibody. Addition of a secondary HRP-conjugated antibody provides sensitive colorimetric readout quantified by spectrophotometry at 450 nm.
Measurement of Maleic dialdehyde (MDA)
Maleic dialdehyde (MDA), a reliable marker for lipid peroxidation, was measured using a thiobarbituric acid assay (Nanjing Jiancheng Bioengineering Institute) according to the manufacturer’s instructions. The total protein content of the samples was measured using a Coomassie Blue assay (Nanjing Jiancheng Bioengineering Institute) and the MDA content (nmol/mg protein) calculated using the following formula: absorbance of sample tube/absorbance of standard tube × 2.5 [9, 10].
Measurement of infiltration of PMN
Meloperoxidase (MPO) activity was measured to assess the extent of PMN infiltration. The samples were stored at −70°C until assay for MPO. The method of assaying MPO activity was according to the guide of the assay kit (Nanjing Jiancheng Bioengineering Co Ltd, China).
Measurement of iNOS and ICAM-1 level
The procedures were processed according to the protocols recommended for inducible nitric oxide synthase (iNOS) and adhesion molecule (ICAM-1) immunohistochemistry kit (Hengdabaisheng Biotechnology, Beijing, China). The samples were exposed to 3% hydrogen peroxide for 10 minutes to bleach endogenous peroxidases. Then microwave oven-based antigen retrieval was performed. Slides were probed with either anti-ICAM-1 (1 :100, rat monoclonal, Hengdabaisheng Biotechnology, Beijing, China) and anti-iNOS (1:100, rat polyclonal, Hengdabaisheng Biotechnology, Beijing, China for 1 hour at 37°C, washed 3 times in PBS, incubated with biotin-labeled anti-rat IgG for 1 hour at 37°C, respectively. Incubation with PBS instead of the primary antibody served as a negative control. After washing in PBS, samples were visualized with 3, 3‘ -diaminobenzidine tetrahydrochloride (DAB) and counterstained with hematoxylin. Finally, the samples were dehydrated in graded ethanol, immersed in xylene and coverslipped. In specimens the positive cells were counted in ten randomly selected areas from each case and expressed as number of immunopositive/mm2.
Measurement of total antioxidant status
The total antioxidant status (TAOS) of serum was determined as previously described by Laight et al. . The increase of absorbance at 405 nm was measured by a microplate reader (Shanghai Xunda Medical Technology, Inc., China).
The data are shown as the mean ± SEM. All data were analyzed by a one-way analysis of variance, and the differences between means were established by Duncan’s multiple-range test. The significant level of 5% (P < 0.05) was used as the minimum acceptable probability for the difference between the means.
Result and discussion
Anti-inflammatory effect of NT on cytokines levels
Effects of NT on NF-κB activation
Effects of NT on Maleic dialdehyde (MDA)
Effects of NT on infiltration of PMN
Effects of NT on iNOS and ICAM-1 level
Effect of NT on ICAM-1and iNOS (number of immunopositive/mm 2 )
10.41 ± 3.88 **
22.22 ± 6.22 **
68.28 ± 9.30
135.11 ± 21.35
53.22 ± 1.22
96.41 ± 21.23
44.22 ± 1.20*
80.41 ± 21.11*
26.36 ± 2.33**
68.41 ± 33.32**
20.30 ± 1.59 **
59.36 ± 26.30 **
Among the immunoglobulin family member, ICAM-1 has been the most extensively investigated in inflammatory process. Patients with acute inflammation had higher soluble ICAM-1 levels compared to patients without disease . The protein expressions of ICAM-1 in the inflammatory group significantly increased compared with those of the control group. NT-2 and NT-4 treatment markedly decreased the level of ICAM-1 as compared to the saline group. (P < 0.05 and P < 0.01, respectively) (Table 1).
Effects of NT on total antioxidant status
Effect of NT on TAOS activity (μM L-ascorbate)
TAOS activity (μM L-ascorbate)
28.41 ± 3.10 **
79.33 ± 7.32
63.22 ± 2.22
48.02 ± 4.22*
36.36 ± 3.33**
35.00 ± 6.60 **
Anti-hyperalgesia effect of NT in animal model
The results demonstrated here provide new evidence that NT has important effects of anti-inflammatory, antioxidant, peripheral antinociceptive and antihyperalgesic activity in animal models of inflammatory pain. The data suggest that NT is a potent anti-inflammatory and analgesic medicine.
This project was supported by NNSF grant (30800301, 31170992, 81102842) and Nature Sciences Foundation of Zhejiang (Y2101127), projects from Key Laboratory of Mental Health, Institute of Psychology and the Knowledge Innovation Program of the Chinese Academy of Sciences (KSCX2-YW-R-254, KSCX2-EW-Q-18 and KSCX2-EW-J-8).
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