Outer Membrane Vesicles of Bordetella pertussis encapsulated into sodium alginate nanoparticles as novel vaccine delivery system

BACKGROUND

Outer membrane vesicles (OMVs) release from Gram-negative bacteria and are interesting alternatives that can replace those vaccines that contain naturally incorporated bacterial surface antigens, lipopolysaccharides (LPS) and outer membrane proteins (OMPs). Nanoparticles can be used to encapsulate vesicles for slow release and prevent macromolecular degradation.

OBJECTIVE

Therefore, encapsulation of OMVs of B. pertussis into sodium alginate nanoparticles was the main aim of the current study.

METHOD

The OMVs of B. pertussis extracted and characterized by particle sizer, electron microscopy, SDSPAGE and Western blot assays. The extracted OMVs were encapsulated in sodium alginate nanoparticles (OMV-NP) using unique gelation process and injected into BALB/c mice. Immunogenicity indices such as different classes of antibodies and interleukins related to different T cell lines were evaluated in immunized mice by ELISA. The respiratory challenge was evaluated in the groups of mice. The existence of pertussis toxin (PTX), filamentous haemagglutinin (FHA) and PRN (pertactin) in B. pertussis OMVs was verified using SDS-PAGE and Western blot analysis.

RESULTS

TEM electron microscopy showed the size of these OMVs to be around 20-80 nm. The OMVs with appropriate quality were encapsulated into sodium alginate nanoparticles (OMV-NP), and the final size was about 500 nm after encapsulation. Immunity indices were significantly higher in the OMV-NP receiving group. In challenge tests, the OMV-NP vaccine was able to show the highest rate of lung clearance compared to the control groups (OMV and wPV) at the lowest injection dose.

CONCLUSION

The results indicate the potential of OMV-NP as a novel vaccine delivery system.

Nanoparticles and Vaccine Development

In spite of the progress of conventional vaccines, improvements are required due to concerns about the low immunogenicity of the toxicity, instability, and the need for multiple administrations of the vaccines. To overcome the mentioned problems, nanotechnology has recently been incorporated into vaccine development. Nanotechnology increasingly plays an important role in vaccine development nanocarrier-based delivery systems that offer an opportunity to increase the cellular and humoral immune responses. The use of nanoparticles in vaccine formulations allows not only enhanced immunogenicity and stability of antigen, but also targeted delivery and slow release. Over the past decade, nanoscale size materials such as virus-like particles, liposomes, ISCOMs, polymeric, inorganic nanoparticles and emulsions have gained attention as potential delivery vehicles for vaccine antigens, which can both stabilize vaccine antigens and act as adjuvants. This advantage is attributable to the nanoscale particle size, which facilitates uptake by Antigen- Presenting Cells (APCs), then leading to efficient antigen recognition and presentation. Modifying the surfaces of nanoparticles with different targeting moieties permits the delivery of antigens to specific receptors on the cell surface, thereby stimulating selective and specific immune responses. This review provides an overview of recent advances in nanovaccinology.

A New Vaccine Delivery Vehicle and Adjuvant Candidate: Bordetella pertussis Inactivated Whole Cells Entrapped in Alginate Microspheres

There is no doubt about the whole cell pertussis vaccine efficacy, but it is necessary to improve the vaccine quality specially to decrease its toxicity by obtaining good immunogenicity with low bacterial content. In this work, under optimum condition inactivated B. pertussis bacteria cells entrapped with alginate microparticles were fabricated and in vivo immunogenicity and ptency of new microparticle based vaccine were evaluated in mice. Microspheres loaded with inactive B. pertussis bacterium cells were prepared via an emulsification method and analyzed for morphology, size, polydispersity index, loading efficiency, loading capacity, release profile and in vivo potency. The inactivated bacterial suspension mixture prepared in this work was nontoxic and showed potent ED50 (1:333 of human dose) and preserved agglutinins 1, 2, 3. The optimum conditions for the preparation of microparticles were achieved at alginate concentration 3.8% (w/v), CaCl2 8% (w/v), PLL 0.1% (w/v), lipophilic surfactant 0.22 (%w/v), hydrophilic surfactant 3.6 (%w/v), cross linking time 3min, homogenization rate 600 rpm, and alginate to CaCl2 solution ratio 4. Both empty and B. pertussis loaded microparticles exhibited smooth surface texture and relatively spherical shape. The B. pertussis encapsulated microspheres fabricated under optimized conditions showed mean particle size 151.1 μm, polydispersity index 0.43, loading efficiency 89.6%, loading capacity 36.3%, and relatively constant release rate lasted to 15 days. In vivo immunogenicity and protection study against wild type challenge showed strongly higher potency (approximately 2.5 fold) of encapsulated B. pertussis organisms than non-encapsulated conventional aluminum hydroxide adsorbed vaccine. It can be concluded that microencapsulation of inactive B. pertussis cells appears to be a suitable approach for improving the wP vaccine quality, specially by obtaining good immunogenicity with low bacterial content.

Hemodynamic Changes in Experimentally Envenomed Anaesthetized Rats by Intravenous Injection of Hemiscorpius lepturus Venom

BACKGROUND

We investigated the hemodynamic changes (Inotropic, chronotropic and arrhythmogenic) in intravenously envenomed anesthetized rats with Hemiscorpius lepturus venom. The neutralizing potencies of different drugs and commercial antivenom were assessed simultaneously.

METHODS

Different doses of the crude venom (100, 200 and 400μg/rat) were injected during five minutes via the femoral vein and cardiovascular changes were recorded in rats in Razi Institute Corporation, Karaj, Iran in 2017. The drugs (Atropine, lidocaine, propranolol and prazosin) were injected before the venom for determination of the counteracting effects. Different volumes (100, 500 and 1000μl) of the antivenom were pre envenomed to neutralize cardiovascular changes.

RESULTS

Temporary hypertension and bradycardia with no arrhythmogenic effects were depicted within twenty minutes. There was a difference in arterial pressure between the venom (400μg/rat) and the vehicle at 8 minutes (114.68±5.1mmHg versus 70.2±4.3mmHg). Elevation of the mean arterial pressure was inhibited by propranolol (2 mg/kg) and neutralized by prazosin (1mg/kg) while lidocaine (4mg/kg) and atropine (1mg/kg) had no effects. Premedication with Iranian commercial antivenom (1000μl) produced surprisingly temporary hypertension compared to the vehicle (140.84±4.5 versus 84.3±3.2). It had no neutralizing properties on blood pressure variation before the venom injection. Volume-expanded hypertension phenomenon was ruled out in a parallel study.

CONCLUSION

This venom has vasoconstrictive effects in rats probably due to the presence of norepinephrine like materials in its content or liberated from adrenal gland inhibited by prazosin premedication. The neutralizing effects of antivenom on venom-induced hypertension are questionable.

A New Approach to Antivenom Preparation Using Chitosan Nanoparticles Containing EchisCarinatus Venom as A Novel Antigen Delivery System

In recent years, use of biodegradable polymers based nanoparticles has received high interest in the development of vaccines delivery vehicles. The aim of study was to prepare chitosan nanoparticles (CS NPs) for loading Echis carinatus (EC) venom and evaluate their potential as an adjuvant and antigen delivery system on a pilot scale. CS NPs were prepared using ionic gelation method, and their characteristics were optimized. Venom-loaded CS NPs prepared under optimum conditions and traditional venom-loaded adjuvants were used to hyperimmunization of horse. Under optimum conditions, particle size, polydispersity index (PDI), and zeta potential of CS NPs were 127.9 ± 15 nm, 0.29, and +19.8 ± 1.92 mV, while those of venom-loaded CS NPs were 182.4 ± 20 nm, 0.35, +26.8 ± 1.98 mv, respectively. All CS NPs had integrated surface and good morphology. Optimum loading concentration of EC venom was 500 µg/mL. The loading capacity (LC) and loading efficiency (LE) were 87% and 94%, respectively, and release profile of venom-loaded CS NPs showed suitable correlation with Higuchi kinetics. Stability test showed good stability of the venom encapsulated in CS NPs. Furthermore, antivenom plasma obtained using the new antigen delivery system had significantly higher potency (P < 0.05) for neutralizing the venom than that obtained using conventional system. These results suggested that venom-loaded CS NPs could be a suitable alternative to conventional adjuvant for development antivenom.

Study on Toxicity Reduction and Potency Induction in Whole-cell Pertussis Vaccine by Developing a New Optimal Inactivation Condition Processed on Bordetella pertussis

Background

Whooping cough is caused by Bordetella pertussis, and it remains a public health concern. Whole-cell pertussis vaccines have been commonly employed for expanded immunization. There is no doubt of the efficacy of whole cell pertussis vaccine, but it is necessary to improve the vaccine to decrease its toxicity.

Objectives

In this study, an inactivation process of dealing with pertussis bacteria is optimized in order to decrease the bacteria content in human doses of vaccines and reduce the vaccine’s toxicity.

Materials and Methods

The bacterial suspensions of pertussis strains 509 and 134 were divided into 21 sample parts from F₁ to F₂₁ and inactivated under different conditions. The inactivated suspensions of both strains were tested for opacity, non-viability, agglutination, purity, and sterility; the same formulation samples that passed quality tests were then pooled together. The pool of inactivated suspensions were analyzed for sterility, agglutination, opacity, specific toxicity, and potency.

Results

The harvest of both bacterial strains showed purity. The opacity of various samples were lost under different treatment conditions by heat from 8% to 12%, formaldehyde 6% to 8%, glutaraldehyde 6% to 8%, and thimerosal 5% to 8%. Tests on suspensions after inactivation and on pooled suspensions showed inactivation conditions not degraded agglutinins of both strains. The samples of F₂, F₄, F₈, F₁₂, F₁₅, and F₁₇ passed the toxicity test. The potency (ED50) of these samples showed following order F₁₇ > F₁₂ > F₈ > F₁₅, F₄ > F₂, and F₁₇ revealed higher potency compared to other formulations.

Conclusions

It can be concluded that F₁₇ showed desirable outcomes in the toxicity test and good immunogenicity with a low bacterial number content. Consequently, lower adverse effects and good immunogenicity are foreseeable for vaccine preparation with this method.

Enteric trimethyl chitosan nanoparticles containing hepatitis B surface antigen for oral delivery

Oral vaccination is the preferred route of immunization. However, the degradative condition of the gastrointestinal tract and the higher molecular size of peptides pose major challenges in developing an effective oral vaccination system. One of the most excellent methods used in the development of oral vaccine delivery system relies on the entrapment of the antigen in polymeric nanoparticles. In this work, trimethyl chitosan (TMC) nanoparticles were fabricated using ionic gelation teqnique by interaction hydroxypropyl methylcellulose phthalate (HPMCP), a pH-sensitive polymer, with TMC and the utility of the particles in the oral delivery of hepatitis B surface antigen (HBsAg) was evaluated employing solutions that simulated gastric and intestinal conditions. The particle size, morphology, zeta potential, loading capacity, loading efficiency, in vitro release behavior, structure, and morphology of nanoparticles were evaluated, and the activity of the loaded antigen was assessed. Size of the optimized TMC/HPMCP nanoparticles and that of the antigen-loaded nanoparticles were 85 nm and 158 nm, respectively. Optimum loading capacity (76.75%) and loading efficiency (86.29%) were achieved at 300 µg/mL concentration of the antigen. SEM images revealed a spherical shape as well as a smooth and near-homogenous surface of nanoparticles. Results of the in vitro release studies showed that formulation with HPMCP improved the acid stability of the TMC nanoparticles as well as their capability to preserve the loaded HBsAg from gastric destruction. The antigen showed good activity both before and after loading. The results suggest that TMC/HPMCP nanoparticles could be used in the oral delivery of HBsAg vaccine.

Study on development of Vipera lebetina snake anti-venom in chicken egg yolk for passive immunization

Chicken egg yolk antibodies against Vipera lebetina venom were evaluated for their antivenom potential. White leghorn hens were immunized with detoxified V. lebetina venom (γ-irradiated venom). The detoxified venom (200 μg) was mixed with an equal volume of complete Freund's adjuvant and was injected intramuscularly into the hens. The antibodies showed high activity (1.6 LD50/mL) in egg yolks after 12 d of venom injection. The eggs were collected after 12 days, and the egg yolks were removed and washed with purified water to remove any contamination with egg whites. The purification was performed using a method described by Maya Devi et al., followed by gel filtration (Sephadex G-50). The purity and molecular weight of antivenom antibodies (IgY) were determined using electrophoresis, and the molecular weight was found to be approximately 185 kDa. The potency of IgY was 6 LD50/mL (mice), i.e., 1 mL of IgY could neutralize 43.8 μg of standard V. lebetina venom). Our results showed that chicken egg yolk antibodies were effective in neutralizing the lethality and several pharmacological effects of V. lebetina venom and could be used for developing effective antivenom.

Study on camel IgG purification: a new approach to prepare Naja Naja Oxiana antivenom as passive immunization for therapy

A combined process of ammonium sulfate precipitation (salting out) and ion-exchange chromatography on DEAE-Sepharose CL-6B was used to prepare camel antivenom (IgG) against Naja Naja Oxiana for therapy. In the ammonium sulfate precipitation, the best condition for fractionation of IgG from the other proteins in camel serum was 55% precipitate. The camel IgG presented as 2 bands with molecular masses of 250 and 100 kDa, the latter corresponding to heavy chain IgG, on 10% gel electrophoresis. A trace amount of non-IgG proteins was not isolated and remained in this precipitate. Therefore in order to effectively separate albumin and the other nonspecific proteins from the IgG, the 25% precipitate of ammonium sulfate precipitation of serum was subjected to DEAE-Sepharose CL-6B column chromatography. A peak of antibody (IgG) could be obtained by elution with sodium phosphate buffer. In this stage, 2 bands of molecular masses of 150 and 75 kDa were observed on 7% gel electrophoresis. A comparative study was performed between camel IgG and conventional horse F(ab) 2 antivenoms in term of potency (serum neutralization test and ELISA). Our results showed that the potency of camel antivenom was 4-fold higher than that of horse. It is suggested the combined ammonium sulfate precipitation and ion-exchange chromatography process effectively removed residual proteins in the final camel IgG preparation and can be a suitable method for large-scale refinement of therapeutic camel antivenoms.