In vivo evidence of angiogenesis inhibition by β2-glycoprotein I subfractions in the chorioallantoic membrane of chicken embryos

The vascular network expansion and functioning are important factors affecting normal intra-uterine fetal development. This study addressed the previously reported antiangiogenic potential of beta-2-glycoprotein I (β2GPI) in vivo in the chick embryo model of angiogenesis. The effects of two naturally occurring β2GPI forms on the development of the chorioallantoic membrane (CAM) vessels and the chicken embryo were investigated. β2GPI monomers and dimers were obtained by fractioned purification and characterized using SDS-PAGE, immunoblot, and ELISA. The egg exposure was performed by injection of small volumes of 2.5 µg/mL solutions of the β2GPI subfractions. Angiogenesis was evaluated through quantitative measurements of vascular architecture parameters in the captured CAM images, using computational analysis of texture contrasts and computer vision techniques. Quantitative information was assigned to the CAM vasculature modifications. In vivo, the β2GPI dimer completely halted the formation of CAM vessels and led to embryo death after 48 h of exposure. The β2GPI monomer allowed the embryo to develop up to the 10th day, despite early changes of CAM vessels. The impaired normal vessel growth proceeded as a self-limited effect. The β2GPI monomer-exposed eggs showed reduced vascularization on the 6th day of incubation, but embryos were viable on the 10th day of incubation, with ingurgitated CAM vessels implying sequelae of the angiogenesis inhibition. Both subfractions impaired CAM vasculature development. The β2GPI dimer proved to be largely more harmful than the β2GPI monomer. β2GPI modification by cleavage or dimerization may play a role in angiogenesis control in vivo.