Regulation of TNF-alpha secretion by a specific melanocortin-1 receptor peptide agonist.

The lack of specific pharmacological tools has impeded the evaluation of the role of each melanocortin receptor (MCR) subtype in the myriad physiological effects of melanocortins. 154N-5 is an octapeptide (MFRdWFKPV-NH(2)) that was first identified as an MC1R antagonist in Xenopus melanophores [J. Biol. Chem. 269 (1994) 29846]. In this manuscript, we show that 154N-5 is a specific agonist for human and murine MC1R. The peptide has negligible activity at MC3R and MC4R and is 25-fold less potent and a weak agonist at MC5R. 154N-5 was tested in both a cellular and an animal model of tumor necrosis factor-alpha (TNF-alpha) secretion. The inhibitory efficacy of 154N-5 on TNF-alpha secretion in both models was similar to the nonselective agonist NDP-alpha-melanocyte stimulating hormone (NDP-alphaMSH), thus, we conclude that inhibition of TNF-alpha secretion by melanocortin peptides is mediated by MC1R. 154N-5 is a valuable new tool for the evaluation of specific contribution of MC1R agonism to physiological and pathological processes.

Ileal bile acid transporter inhibition, CYP7A1 induction, and antilipemic action of 264W94.

264W94 was designed to inhibit the ileal bile acid transporter (IBAT). Evaluated in vitro, 264W94 dose-dependently inhibited sodium-dependent uptake of 10 micro M [(3)H]taurocholic acid (TC) by rat and monkey brush border membrane vesicles with IC(50)s of 0.24 micro M and 0.41 micro M, and had a competitive profile with K(i) of 0.2 micro M against TC in Chinese hamster ovary cells expressing human IBAT. In distal ileum in situ, 1-10 micro M of 264W94 rapidly decreased uptake of 3mM TC by 24-39%, with corresponding decreases in biliary recovery. In rats and mice in vivo, oral 264W94 decreased absorption of TC analog, 23,25-(75)Se-homocholic acid taurine ((75)SeHCAT; quantitated in feces), with ED(30) of 0.02 mg/kg bid. (75)SeHCAT traced through the GI-tract revealed that peak (97%) inhibition of (75)SeHCAT absorption by the distal quarter of small intestine occurred at 4 h after single dose of 264W94 (0.1 mg/kg). Inhibition of IBAT by 264W94 in rats was associated with compensatory, same-day, 4-fold induction of hepatic cholesterol 7alpha-hydroxylase (CYP7A1) activity, exhibiting normal diurnal fluctuation for 3 days of dosing. In diet induced hypercholesterolemic rats, 264W94 (0.03-1.0 mg/kg bid) dose-dependently reduced serum LDL+VLDL cholesterol up to 61%. In conclusion, 264W94 is a potent new cholesterol lowering agent that acts through inhibition of IBAT and exhibits activity in a human model.