Polysaccharide microparticles as carriers of a recombinant antigen against GnRH in oral vaccination of male rats

Abstract

Polysaccharide microparticles (PSMs) are a promising carrier system for the oral administration of antigens. They can protect antigens from degradation in the harsh environment of the gut. They can also improve the uptake of antigens by the immune system. Anti-GnRH vaccines work by blocking the binding of GnRH to its receptors on the cells of the hypothalamus and pituitary gland, preventing the release of LH and FSH and consequently suppress sex hormone production. Anti-GnRH injectable vaccines have been developed for a variety of production animals as an alternative to surgical castration. In this work we orally delivered polysaccharide microparticles containing a recombinant fusion protein as an antigen to develop Anti-GnRH response in male rat. We designed and expressed a recombinant 45 KDa peptide (GF45) consisting of a 4 tandem repeats from the GnRH sequence EHWSYGLRPG fused to an immunogenic carrier peptide which contains rickettsial Hsp70 and Hsp60 sequences. GF was encapsulated in alginate-chitosan particles by ionic reverse gelation. Particles containing 200 ug of recombinant peptide were orally administrated to a group of 4-week year old male Sprague-Dowley rats (n=10) in a prime-boost immunization scheme. Empty particles and injectable GF were used as controls. Serum testosterone and anti-GF45 antibodies were analysed by ELISA method along with the weight and volume of testicles. The GF45 orally treated group showed detectable titters of anti-GF45 antibodies and a 95% reduction of circulating testosterone in comparison to the control group. Testicles in treated group showed a reduction of 52% in weight and 50% in volume regarding to control. The encapsulation and oral delivery of the recombinant GF45 in alginate-chitosan microparticles generated autoimmune response capable of blocking the function of endogen GnRH. These particles are a suitable not only for generating non injectable or surgical control of GnRH but also to possibly deliver other recombinant antigens.