Biological characterisation of somatropin-derived cryptic peptides

Abstract

Little is known about possible cryptic peptides of the recombinant growth hormone (somatropin). In this study, six synthetic somatropin-derived peptides (SDPs) were selected based on their sequences which correspond to the binding interface of the growth hormone receptor (GHR). Their novelty was confirmed by in silico and in vitro proteolytic digestion of somatropin. Chemical characterisation of the SDPs, i.e. identification via LC–MS and purity quantification via HPLC-UV and U(H)PLC-MRM, was first performed. All the SDPs were stable in brain tissue homogenate, liver tissue homogenate and serum (t1/2 > 15 min). The metabolites in brain and serum, formed between 15 and 120 min, were also identified. The interactions towards the GHR and the human growth hormone binding protein (hGHBp) were also evaluated using GHR bioassay and native MS. No interaction was detected under the applied conditions. A last part of the study investigated the pharmacokinetics and tissue distribution of two peptides (i.e. SDP167–175 and SDP101–121), selected based on their position within somatropin. A high blood–brain barrier (BBB) influx was observed for SDP101–121, while SDP167–175 showed a negligible BBB influx. Based on the obtained results, the GHR binding of the selected SDPs is very low, requiring structural adaptations for further GHR-binding exploration.