Animal experiment:

Mice[1]Mice are treated from day 1 post-ovariectomy for 4 weeks with LP-533401 (1, 10, 100 or 250 mg per kg body weight per day) or vehicle. Next mice are treated for 4 weeks starting 2 weeks post-ovariectomy with LP-533401 (250 mg per kg body weight per day) or vehicle. lastly, mice are treated for 6 weeks starting 6 weeks post-ovariectomy with LP-533401 (25, 100 or 250 mg per kg body weight per day) or vehicle[1].

LP533401 hcl is an inhibitor of Tph-1 [1].

Tryptophan hydroxylase-1 (Tph-1) is an isoenzyme of tryptophan hydroxylase and the initial enzyme in gut- and lung-derived serotonin biosynthesis. Tph-1 is mainly expressed in the gut and lung [2].

LP533401 hcl is a Tph-1 inhibitor. In rat RBL2H3 cells expressing Tph1, LP533401 (1 μM) completely inhibited serotonin production. LP533401 reduced the activity of recombinant wild-type TPH-1 by 70% by interacting with residues Tyr235 and Phe241 [1].

In rodents, LP533401 orally administration was incapable of crossing the blood-brain barrier. In mice, LP533401 (250 mg/kg) dose-dependently reduced serum serotonin concentration by 30%. In ovariectomized female C57BL6/J mice, LP533401 (10, 100, 250 mg/kg for 28 days) increased bone mass and bone-formation parameters such as osteocalcin serum concentration, osteoblast numbers and bone formation rate. Also, LP533401 dose-dependently decreased serum serotonin concentration but didn’t affect brain serotonin content. In ovariectomized female rats, LP533401 completely rescued the ovariectomy-induced osteopenia [1]. In transgenic SM22-5-HTT+ mice overexpressing 5-HT transporter (5-HTT) in smooth muscle cells and spontaneously developing pulmonary hypertension (PH), LP533401 (250 mg/kg for 21 days) significantly reduced lung and blood 5-HT levels, vascular Ki67-positive cells, distal pulmonary artery muscularization, right ventricular (RV) hypertrophy and RV systolic pressure [2].

References:
[1]. Yadav VK, Balaji S, Suresh PS, et al. Pharmacological inhibition of gut-derived serotonin synthesis is a potential bone anabolic treatment for osteoporosis. Nat Med, 2010, 16(3): 308-312.
[2]. Abid S, Houssaini A, Chevarin C, et al. Inhibition of gut- and lung-derived serotonin attenuates pulmonary hypertension in mice. Am J Physiol Lung Cell Mol Physiol, 2012, 303(6): L500-508.