Effect of Novel Melanocortin Type 2 Receptor Antagonists on the Corticosterone Response to ACTH in the Neonatal Rat Adrenal Gland In Vivo and In Vitro

Abstract

Stress-induced increases in neonatal corticosterone demonstrate a unique shift from ACTH independence to ACTH dependence between postnatal day 2 (PD2) and day 8 (PD8) in newborn rats. This shift could be due to the binding of a bioactive, non-­immunoreactive plasma ligand to the adrenocortical melanocortin 2 receptor (MC2R) (ACTH receptor). A potent MC2R antagonist would be useful to evaluate this phenomenon in the neonate. Therefore, we investigated the acute corticosterone response to ACTH(1–39) injection in rat pups pretreated with newly developed MC2R antagonists (GPS1573 and GPS1574), which have not been tested in vivo. The doses used in vivo were based on their in vitro potency, with GP1573 being more potent than GPS1574. GPS1573 (PD2 and PD8), GPS1574 (PD2 only), or vehicle were injected intraperitoneally (ip) 10 min before baseline sampling. Then, 0.001 mg/kg of ACTH(1–39) was injected ip, and subsequent blood samples obtained for the measurement of plasma corticosterone. Pretreatment of PD2 pups with GPS1573 demonstrated augmentation, rather than inhibition, of the corticosterone response to ACTH. In PD8 pups, pretreatment with 0.1 mg/kg GPS1573, but not 4 mg/kg, augmented the corticosterone response to ACTH. Pretreatment with GPS1574 attenuated the plasma corticosterone response to ACTH at 30 min in PD2 pups. The activity of these two compounds in vivo do not match their potency in vitro, with GPS1573 leading to a small augmentation of the corticosterone response to ACTH in vivo while GPS1574 resulted in inhibition.

Pathological cyclic strain promotes proliferation of vascular smooth muscle cells via the ACTH/ERK/STAT3 pathway

“…Many studies have shown that the receptor of ACTH is a G‐protein‐coupled receptor, which may participate in a series of downstream protein phosphorylation events . Thus, the classical phosphorylation of the ERK/STAT3 pathway was examined in VSMCs.…”

“…Many studies have shown that the receptor of ACTH is a G-protein-coupled receptor, which may participate in a series of downstream protein phosphorylation events. 16 Thus, the classical phosphorylation of the ERK/STAT3 pathway was examined in VSMCs. The results showed that when VSMCs were treated with ACTH (1000 nM), ERK phosphorylation was significantly up-regulated after 15 min of treatment, while STAT3 phosphorylation at the Ser727 residue was up-regulated after 30 min ( Figure 2B-D).…”

“…MC2R is confined to the endoplasmic reticulum and cannot localize to the cell membrane when the cell lacks MRAP . The activated MC2R activates Gα s by depolymerizing the downstream trimeric G protein, facilitating its guanylate conversion, activating adenylate cyclase, causing the accumulation of cAMP, and finally mediating the phosphorylation of downstream molecules . However, whether ACTH promotes VSMC proliferation via MC2R remains to be elucidated.…”

Treating canine Cushing’s syndrome: Current options and future prospects

“…A recent study showed that two ACTH analogs, GPS1573 and GPS1574, are potent antagonists of the MC2R in vitro. However, these peptides also had some agonistic and/or antagonistic effects on other melanocortin receptors, and subsequent studies in rats showed disappointing results in vivo (Bouw et al, 2014;Nensey et al, 2016). Further developments might eventually generate a selective MC2R antagonist that could be used as a medical treatment option in dogs with PDH.…”

ACTH Antagonists

“…They also conducted in vivo experiments in young rats but were unable to show inhibition of the ACTH response even at 400-fold molar excess of antagonist in the case of GPS1573. GPS1574 was partially inhibitory at 30 min after ACTH injection ( 59 ).…”