The in vivo anti-fibrotic function of calcium sensitive receptor (CaSR) modulating poly(p-dioxanone-co-l-phenylalanine) prodrug

In present study, the apoptosis induction and proliferation suppression effects of l -phenylalanine ( l -Phe) on fibroblasts were confirmed. The action sites of l -Phe on fibroblasts suppression were deduced to be calcium sensitive receptor (CaSR) which could cause the release of endoplasmic reticulum (ER) Ca2+ stores; disruption of intracellular Ca2+ homeostasis triggers cell apoptosis via the ER or mitochondrial pathways. The down-regulation of CaSR were observed after the application of l -Phe, and the results those l -Phe triggered the increasing of intracellular Ca2+ concentration and calcineurin expression, and then the apoptosis and increasing G1 fraction of fibroblasts have verified our deduction. Hence, l -Phe could be seen as a kind of anti-fibrotic drugs for the crucial participation of fibroblast in the occurrence of fibrosis. And then, poly(p-dioxanone-co- l -phenylalanine) (PDPA) which could prolong the in-vivo anti-fibrotic effect of l -Phe for the sustained release of l -Phe during its degradation could be treated as anti-fibrotic polymer prodrugs. Based on the above, the in vivo anti-fibrotic function of PDPA was evaluated in rabbit ear scarring, rat peritoneum lipopolysaccharide, and rat sidewall defect/cecum abrasion models. PDPA reduced skin scarring and suppressed peritoneal fibrosis and post operation adhesion as well as secretion of transforming growth factor-β1 in injured tissue. These results indicate that PDPA is an effective agent for preventing fibrosis following tissue injury. Statement of Significance We have previously demonstrated that poly(p-dioxanone-co- l -phenylalanine) (PDPA) could induce apoptosis to fibroblast and deduced that the inhibitory effect comes from l -phenylalanine. In present study, the inhibition mechanism of l -phenylalanine on fibroblast proliferation was demonstrated. The calcium sensitive receptor (CaSR) was found to be the action site. The CaSR was downregulated after the application of l -phenylalanine, and then the ER Ca2+ stores were released. The released Ca2+ can simultaneously activate Ca2+/calcineurin and then trigger apoptosis and G1 arrest of fibroblast. Hence, l -phenylalanine could be seen as anti-fibrosis drug and PDPA which conjugate l -phenylalanine by hydrolytic covalent bonds could be seen as l -phenylalanine polymer prodrug. Based above, the in vivo anti-fibrotic function of PDPA were verified in three different animal models.