Biological and immunological characteristics of porcine follicle-stimulating hormone chemically modified with a polyethylene glycol derivative.

Porcine follicle-stimulating hormone (pFSH) was chemically modified with a polyethylene glycol (PEG) derivative to form PEGylated pFSH. The hormone was conjugated with a succinimidyl ester of methoxy PEG propionic acid (mPEG-SPA) at stoichiometric molar ratios of 1:0, 1:1, 1:3, 1:10, 1:30 and 1:100. The molecular weight of PEGylated pFSH increased depending on the stoichiometry of the conjugation reaction. Western blot analysis revealed a multifarious ladder-pattern of PEGylated pFSH with apparent molecular weights of 31, 44, 66, 90 and 115 kDa. Differences between the immunopositive bands mostly coincided with the multiple of 5000 that was the molecular size of mPEG-SPA. PEGylated pFSH was biologically active and capable of stimulating both proliferation of and progesterone secretion by cultured bovine cumulus cells. PEGylated pFSH did not react with antibody against bovine FSH in a binding assay. The results indicate that PEGylated pFSH is still bioactive although this activity is reduced and the elimination of immunoreactivity by PEGylation suggests this modification may have merit in creating a product useful in inducing bovine superovulation.