Expression, purification and development of neutralizing antibodies from synthetic BoNT/B LC and its application in detection of botulinum toxin serotype B

Botulism is a neuroparalytic disease caused by Clostridium botulinum, which produces seven (A-G) neurotoxins (BoNTs). The mouse bioassay is the gold standard for the detection of botulinum neurotoxins, however it requires at least 3-4 days for completion. Most of the studies were carried out in botulinum toxin A and less on type B. Attempts have been made to develop an ELISA based detection system, which is potentially an easier and more rapid method of botulinum neurotoxin detection. In the present study, the synthetic BoNT/B LC gene was constructed using PCR overlapping primers, cloned in a pET28a+ vector and expressed in E. coli BL21DE3. The maximum yield of recombinant proteins was optimized after 16 hrs of post induction at 21°C and purified the recombinant protein in soluble form. Antibodies were raised in Mice and Rabbit. The IgG antibody titer in the case of Mice was 1: 1,024,000 and Rabbit was 1: 512,000 with alum as adjuvant via intramascular route. The biological activity of the recombinant protein was confirmed by in-vitro studies using PC12 cells by the synaptobrevin cleavage, the rBoNT/B LC protein showed the maximum blockage of acetylcholine release at a concentration of 150nM rBoNT/B LC in comparison to the control cells. When the cells were incubated with rBoNT/B LC neutralized by the antisera raised against it, the acetylcholine release was equivalent to the control. IgG specific to rBoNT/B LC was purified from raised antibodies. The results showed that the developed antibody against rBoNT/B LC protein were able to detect botulinum toxin type B approximately up to 1 ng/ml. These developed high titer antibodies may prove useful for the detection of botulinum neurotoxins in food and clinical samples.

Recombinant Shiga toxin B subunit elicits protection against Shiga toxin via mixed Th type immune response in mice

Shigella dysenteriae is the causative agent of the third commonest bacterial disease for childhood diarrhoea and responsible for millions of deaths per year. It produces potent toxin termed Shiga toxin which is listed in category B biological warfare agent of CDC, USA. Earlier we have reported production of recombinant Shiga toxin B subunit that produced antibodies which neutralized Shiga toxin toxicity in HeLa cells. In the present study, we have evaluated the immunomodulatory potential of rStxB protein in Balb/c mice using Freunds adjuvants. Animal protection with recombinant StxB was conferred through both humoral and cellular immune responses as indicated by an increased antibody titre with predominance of IgG2a and IgG2b isotypes along with elevated levels of IgG1 subtype. Cytokine profile of the mice antiserum and splenocyte also indicates Th2 and Th1 type of immune responses where former dominates in early stage of immunization. Histopathology study of kidneys of vaccinated mice showed remarkable differences when compared to the animals infected with Shigella dysenteriae type1. The present study indicates that recombinant StxB is a promising vaccine candidate and can be used for production of therapeutic antibodies to counter Shiga intoxication.

Development of immunodetection system for botulinum neurotoxin type B using synthetic gene based recombinant protein

BACKGROUND & OBJECTIVES

Botulinum neurotoxins (A-G) are among most poisonous substances in the world, produced by obligate anaerobic bacteria Clostridium botulinum. Among the seven serotypes A, B, E and F are of human importance. In India, the prevalence of C. botulinum as well as botulism outbreaks have been reported. Due to its extreme toxicity it has been classified in the Category A of biological warfare agent. So far, there is no commercial detection system available in India to detect botulism. The present study aims to develop an immuno detection system for botulinum neurotoxin serotype B using synthetic gene approach.

METHODS

The truncated fragment of the botulinum neurotoxin type B from amino acid 1-450 was synthesized using PCR overlap primers; the constructed gene was cloned in the pQE30UA vector and transformed to Escherichia coli SG 13009. The recombinant protein expression was optimized using various concentration of isopropylthiogalactoside (IPTG) induction, further the expression was confirmed by Western blot analysis using anti-His antibody. Recombinant protein was purified under denatured condition using Ni-NTA affinity chromatography. Antibody was generated against the recombinant protein using alum adjuvant in BALB/c mice and tested for cross reactivity with other serotypes of C. botulinum as well as closely related clostridia. An ELISA test was developed for the detection of botulinum neurotoxin and the minimum detection limit was also estimated.

RESULTS

The recombinant protein was expressed at maximum yield at 4.3 h of post-induction with 0.5 mM IPTG concentration. The recombinant protein was purified using Ni-NTA affinity chromatography up to the homogeneity level. The polyclonal antibodies were raised in mice with a titre of 1:2,048,000. The developed antibody was highly specific with a sensitivity of detecting approximately 15 ng/ml of recombinant protein and not showing any cross-reactivity with other serotypes.

INTERPRETATION & CONCLUSIONS

There is no commercial immunodetection system available in India to detect botulism. The developed detection system is highly specific. It will be useful for growing food industry to detect botulinum neurotoxin in food samples as well as in clinical samples.

Rapid multiplex PCR assay for the simultaneous detection of the Brucella Genus, B. abortus, B. melitensis, and B. suis

The routine identification and differentiation of Brucella species is a time-consuming and labor-intensive process, which frequently places personnel at risk of laboratoryacquired infection. Here, we describe the development of a rapid multiplex PCR assay for the confirmation of presumptive Brucella isolates. The assay was able to identify and differentiate major human pathogens, namely B. abortus, B. melitensis, and B. suis, in a single test of less than an hour and a half.

Differential toxicity profile of ricin isoforms correlates with their glycosylation levels

Ricin is one of the most potent and deadly plant toxins from the seeds of Ricinus communis. In view of its high toxicity, ricin is being used as an immunotoxin in cancer therapy. Ricin also has several isoforms with differential glycosylation depending on the seed variety. Our study shows three isoforms designated 1, 2 and 3, which differed in their surface charge, resulting in a different behavior on cation exchange chromatography, two dimensional (pI 5.5-8.7) and native PAGE. The molecular masses of isoform-1, 2 and 3 were measured as 63.55 kDa, 64.03 kDa and 62.8 kDa, respectively, by MALDI-TOF/MS. In vitro studies with monkey kidney (Vero) cells showed a time dependent increase in cytotoxicity of the isoforms evaluated by extracellular lactate dehydrogenase activity and mitochondrial dehydrogenase assay. These isoforms also induce oxidative stress and DNA damage. Among the isoforms, isoform-3 was quick to generate reactive oxygen species (ROS), (in 90 min) and exhibited maximum cytotoxicity. Morphological changes, catalase activity and DNA fragmentation were significantly higher with isoform-3 treatment compared to others. The glycosylation studies by MALDI-TOF/MS showed that isoform-3 is highly glycosylated with high sugar levels containing more of hybrid/complex type glycopeptides with mannose as hexose units. These experimental evidences clearly suggest that isoform-3 is superior in its early ROS generation, potency to induce oxidative stress and cytotoxicity, that could be due to it's higher glycosylation levels which make isoform-3 as an ideal candidate for immunotoxin studies.

Purification, characterization and toxicity profile of ricin isoforms from castor beans

The castor seed contains the toxin ricin, one of the most poisonous naturally occurring toxins. The whole of the plant is poisonous, however the seeds are considered the major source of ricin. Ricin exists in different forms in beans of different origin. We investigated the presence of ricin in different isoforms and elucidate some of their structural and biological features isolated from the castor seeds. The isoforms were sub fractionated into ricin I, II and III by chromatography. Their molecular weights lie between 60-65 kDa with difference in their relative electrophoretic mobility. An acidic native PAGE of ricin isoforms at pH 2.9 was performed. Ricin I, II and III are highly cytotoxic against Vero cell line with IC(50) values of 60, 30 and 8 ng/ml respectively. Difference in cytotoxicity of isoforms was confirmed through hemagglutination assay, ricin III caused high degree of hemolysis. The preliminary in vivo toxicity studies showed that ricin III is highly toxic. Immunological studies revealed that anti-ricin I and II antibodies are cross reactive with all the ricin variants, whereas the anti-ricin III antibody is highly specific. The present study shows that anti-ricin I and II antibodies can be used for detection of entire ricin isoforms.

Characterization of native and denatured ricin using MALDI-TOF/MS

Ricin is a toxic protein present in the seeds of castor bean plant. It can be inactivated by heat; therefore characterization of denatured ricin is essential to differentiate it from native ricin and to avoid any ambiguity in its identification. In this study, potential of mass spectrometry using MALDI—TOF/MS has been exploited to investigate the effects of heat treatment on ricin and spiked food matrices. The molecular weights of ricin, ricin A (A1 and A2) and B chain were found to be 62.8 kDa, 31.2 kDa, 32.5 kDa and 32 kDa respectively. The mass spectrum revealed a polypeptide chain of 11.1 kDa for denatured ricin. The peptide mass fingerprinting showed 24 peptides, six were common both in native and denatured ricin. The differentiating peptide at position 294—318 (m/z 934.533) was observed only in denatured ricin. The three selected marker peptides m/z 1013.6, 1310.7, 1728.9 are chosen for identification of ricin inactivated by heat in spiked apple juice and milk samples by immunocapture analysis. There is always a probability of denatured non— toxic ricin being confused with native (toxic) ricin to create unnecessary panic. Keeping this probability in mind, our study will be of immense value in minimising such risk.

Denatured ricin can be detected as native ricin by immunological methods, but nontoxic in vivo

Ricin is a glycoprotein from Ricinus communis seeds. It is known to have diverse toxic effects on cells of different visceral organs. In the present study, we purified and denatured ricin in a boiling water bath for different time intervals. We further made an attempt to identify native and denatured ricin by immunobased detection systems. All the antigen/antibody-based assays identified native and denatured ricin. On SDS-PAGE, only native ricin was observed. In western blotting, ricin boiled for 3.75 min gave a strong band on X-ray film. On native polyacryl amide gel electrophoresis, native and denatured ricin gave ricin band in 60-kDa region. The denatured ricin did not [corrected] cause mortality up to 25 mg/kg, while 5 and 10 microg/kg of native ricin caused 50% and 100% mortality, respectively. Detection of native and denatured ricin is very difficult, and the investigating agencies, forensic scientists, and analysts should be very careful while interpreting the results.

Molecularly imprinted nanopatterns for the recognition of biological warfare agent ricin

Molecularly imprinted polymer (MIP) for biological warfare agent (BWA) ricin was synthesized using silanes in order to avoid harsh environments during the synthesis of MIP. The synthesized MIP was utilized for the recognition of ricin. The complete removal of ricin from polymer was confirmed by fluorescence spectrometer and SEM-EDAX. SEM and EDAX studies confirmed the attachment of silane polymer on the surface of silica gel matrix. SEM image of Ricin-MIP exhibited nanopatterns and it was found to be entirely different from the SEM image of non-imprinted polymer (NIP). BET surface area analysis revealed more surface area (227 m(2)/g) for Ricin-MIP than that of NIP (143 m(2)/g). In addition, surface area study also showed more pore volume (0.5010 cm(3)/g) for Ricin-MIP than that of NIP (0.2828 cm(3)/g) at 12 nm pore diameter confirming the presence of imprinted sites for ricin as the reported diameter of ricin is 12 nm. The recognition and rebinding ability of the Ricin-MIP was tested in aqueous solution. Ricin-MIP rebound more ricin when compared to the NIP. Chromatogram obtained with Ricin-MIP exhibited two peaks due to imprinting, however, chromatogram of NIP exhibited only one peak for free ricin. SDS-PAGE result confirmed the second peak observed in chromatogram of Ricin-MIP as ricin peak. Ricin-MIP exhibited an imprinting efficiency of 1.76 and it also showed 10% interference from the structurally similar protein abrin.

Dose dependent effect of ricin on DNA damage and antioxidant enzymes in mice

Ricin a glycoprotein from the Ricinus communis seeds, is known to have diverse toxic effects on cells of different visceral organs. We have studied the effect of ricin (0.5, 1.0 and 2.0 LD50) on various oxidative stress markers at 1, 3 and 7 day post exposure following i.p. administration in Swiss albino male mice. Results of this study revealed that ricin induces generation of reactive species, lipidperoxidation, DNA fragmentation and depletion of GSH. Activity of antioxidant cascade related enzyme like superoxide dismutase (SOD), glutathione peroxidase (GPx) decreased, while glutathione reductase (GR) and catalase activity increased. Superoxide dismutase and glutathione peroxidase activity was decreased significantly in liver, spleen and kidney. The decrease was more prominent on 7 day of post exposure in all the exposed doses. A significant increase in the activities of catalase was observed in plasma, liver, spleen and kidney on 7 day following ricin exposure. Glutathione reductase increased significantly as early as 24 h following 1.0 LD50 dose. Lipid peroxidation increased and non protein sulfhydryl content decreased in all the tissues at different time intervals. Total antioxidant status was reduced as early as 1 day post exposure. Nearly two fold increase was observed in DNA fragmentation following 0.5 LD50 dose of ricin on 1 day post exposure. DNA diffusion assay also indicated an early damage to DNA due to ROS. An early change in DNA fragmentation, DNA diffusion, and total antioxidant status and in the activity of various enzymes indicates that ricin produce oxidative stress by generation of reactive oxygen species as early as 24 h at a minimum dose of 0.5 LD50. Probably this is the first study which indicate that ricin induced oxidative stress at a minimum dose of 0.5 LD50.

Protective effect of ethanolic and water extracts of sea buckthorn (Hippophae rhamnoides L.) against the toxic effects of mustard gas

Ethanolic extract of H. rhamnoides L. leaf (HL-EOH), water and ethanolic extract of H. rhamnoides fruit (HF-W and HF-EOH), and H. rhamnoides flavone from fruit (HR-flavone) were evaluated against percutaneously administered sulphur mustard (SM), a chemical warfare agent. The animals administered with SM (9.7, 19.3 and 38.7 mg/kg) died at various days depending upon the dose and there was a significant reduction in the body weight. The H. rhamnoides extracts (1 g/kg; 3 doses; po) significantly protected the lethality, with a protective index of 2.4, 1.7, 1.7 and 2.2 for HL-EOH, HF-W, HF-EOH and HR-flavone respectively. Reduced glutathione (GSH) and oxidized glutalthione (GSSG) levels were reduced, and malondialdehyde (MDA) was elevated after percutaneous administration of SM. Oral administration of HL-EOH and HR-flavone significantly protected the body weight loss. Recovery in the levels of GSH, GSSG and MDA were also observed following oral administration of HL-EOH and HR-flavone. All the extracts were non-toxic and the LD50 was more than 5 g/kg. The present study shows that percutaneous administration of SM induces oxidative stress and ethanolic extract of leaf of H. rhamnoides and H. rhamnoides flavone from fruit can significantly protect it.

Effect of sub-acute oral cyanide administration in rats: Protective efficacy of alpha-ketoglutarate and sodium thiosulfate

Chronic toxicity of cyanide in humans and animals has been previously described. Alpha-ketoglutarate (alpha-KG) and sodium thiosulfate (STS) are known to confer remarkable protection against acute cyanide poisoning in rodents. Their efficacy against sub-acute or chronic cyanide exposure is not known. The objective of the present study was to assess the sub-acute toxicity of potassium cyanide (KCN) in female rats following oral administration of 7.0 mg/kg (0.5 LD50) for 14 d. The effect of alpha-KG (oral; 1.0 g/kg) and/or STS (intraperitoneal, 1.0 g/kg) on cyanide toxicity was also evaluated. Various hematological and biochemical indices were determined after 7 d of treatment and additional parameters like organ-body weight index (OBI) and histology of brain, heart, lung, liver, kidney and spleen were performed after 14 and 21 d (recovery group) of cyanide exposure. Sub-acute exposure of KCN did not produce any significant change in body weight of the animals, OBI, hematology and the levels of blood urea, creatinine, aspartate aminotransferase, triiodothyronine (T3) and tetraiodothyronine (T4). The levels of temporal glutathione disulfide (GSSG) and hepatic malondialdehyde (MDA), reduced glutathione (GSH) and GSSG were unaffected. However, in KCN treated animals elevated levels of blood glucose and reduced levels of alanine aminotransferase were observed. Activities of cytochrome c oxidase in the brain and rhodanese in the liver were diminished. Reduced levels of GSH and enhanced levels of MDA in brain were observed. Increased levels of blood thiocyanate were observed in all the treatments of KCN. Additionally, KCN also produced various histological changes in the brain, heart, liver and kidney. Although, treatment of alpha-KG and STS alone significantly blunted the toxicity of KCN, concomitant use of both interventions afforded to maximum protection. This study indicates a promising role of alpha-KG and STS for the treatment of prolonged cyanide exposures.

Mechanism of ricin-induced apoptosis in human cervical cancer cells

The mechanism of ricin-induced apoptosis in human cervical cancer cell line HeLa was studied. The present study demonstrated that ricin induces apoptosis of human cervical cancer cells (HeLa) in a time dependent manner with an IC(50) for cell viability of 1 microg/ml. Ricin treatment resulted in a time dependent increase in LDH leakage, DNA fragmentation, percent apoptotic cells, generation of reactive oxygen species and depletion of intracellular glutathione levels. DNA agarose gel electrophoresis showed typical oligonucleosomal length DNA fragmentation. Additionally, DNA diffusion assay was performed to confirm DNA damage and apoptosis. Ricin activated caspase-3 as evidenced by both proteolytic cleavage of procaspase-3 into 20 and 18 kDa subunits, and increased protease activity. Caspase activity was maximum at 4h and led to the cleavage of 116 kDa poly(ADP-ribose) polymerase (PARP), resulting in the 85 kDa cleavage product. Ricin-induced caspase-3 activation also resulted in cleavage of DNA fragmentation factor-45 (DFF45/ICAD) and DFF40 or caspase-activated DNase in HeLa cells. Activation of caspase-3, cleavage of PARP and DNA fragmentation was blocked by pre-treatment with caspase-3 specific inhibitor Ac-DEVD-CHO (100 microM) and broad-spectrum caspase inhibitor Z-VAD-FMK (40 microM). Ricin-induced DNA fragmentation was inhibited by pre-treatment with PARP inhibitors 3-aminobenzamide (100 microM) and DPQ (10 microM). Our results indicate that ricin-induced cell death was mediated by generation of reactive oxygen species and subsequent activation of caspase-3 cascade followed by down stream events leading to apoptotic mode of cell death.

Oxidative stress associated hepatic and renal toxicity induced by ricin in mice

Ricin a glycoprotein from the Ricinus communis seeds, is known to have diverse toxic effects on cells of different visceral organs. We have studied the hepatotoxicity, nephrotoxicity, and oxidative stress following i.p. administration of ricin (25 microg/kg) in Swiss albino male mice. The results of this study revealed that activities of various enzymes like glutamic pyruvic transaminase (GPT), alkaline phosphatase (ALP), gamma glutamyl transpeptidase (gamma-GT), and lactate dehydrogenase (LDH) were increased in plasma, liver, and kidney tissues indicating damage in liver and kidney. Blood urea level was also increased. However, blood creatinine and bilirubin were not altered. Lipid peroxidation increased to 49 and 25% in hepatic and renal tissue. Total non-protein sulfhydryl content decreased in plasma (12%), hepatic (29%), and renal (16%) tissues. Superoxide dismutase activity decreased significantly in liver (43%) and kidney (37%). The activity of glutatione peroxidase was also decreased. The decrease was more prominent in kidney than liver. A significant increase, 20 to 27% in the activity of catalase was observed in plasma, liver, and kidney. These results indicate that ricin produces hepatoxicity, nephrotoxicity, and oxidative damage at 24 h of post treatment. The hepatotoxicity was more prominent than nephrotoxicity.

Covert bacteriuria in nephrotic syndrome

Prevalence of covert bacteriuria in patients of nephrotic syndrome admitted for kidney biopsy was studied in 205 patients. Age ranged from 10 years to 65 years. 148 patients were male and 57 were female. Prevalence of covert bacteriuria was found in 38 patients (18.53%). In bacteriuric patients 30 were male, 8 were female. Escherichia coli was the commonest organism grown in bacteriuric patients (30 or 78.9%). Serum albumin was low and 24-hour urinary protein excretion was high in bacteriuric patients in comparison to abacteriuric patients. In bacteriuric patients membranous nephropathy was the commonest histopathological finding present in 15 patients (39.47%).

Covert bacteriuria in nephrotic syndrome

Prevalence of covert bacteriuria in patients of nephrotic syndrome admitted for kidney biopsy was studied in 205 patients. Age ranged from 10 years to 65 years. 148 patients were male and 57 were female. Prevalence of covert bacteriuria was found in 38 patients (18.53%). In bacteriuric patients 30 were male, 8 were female. Escherichia coli was the commonest organism grown in bacteriuric patients (30 or 78.9%). Serum albumin was low and 24-hour urinary protein excretion was high in bacteriuric patients in comparison to abacteriuric patients. In bacteriuric patients membranous nephropathy was the commonest histopathological finding present in 15 patients (39.47%).