Melanin-concentrating hormone-1 receptor binding activity of pheophorbides isolated from Morus alba leaves.

The time-resolved fluorescence technique based on melanin-concentrating hormone (MCH) receptor subtype-1 (MCH-1 receptor) binding assay was adopted to carry out a bioassay-guided fractionation of the methanol extract of Morus alba leaves. This fractionation and purification led to the isolation of two compounds identified as pheophorbide a methyl ester and 13(2)(S)-hydroxypheophorbide a methyl ester. These active pheophorbides exhibited potent inhibitory activity in binding of europium-labeled MCH to the human recombinant MCH-1 receptor (IC(50) value; 4.03 and 0.33 microM, respectively). Besides binding activity, the pheophorbides inhibited MCH-mediated extracellular signal-regulated kinase (ERK) phosphorylation in Chinese hamster ovary cells expressing human MCH-1 receptor. These results suggest that pheophorbide a methyl ester and 13(2)(S)-hydroxypheophorbide a methyl ester act as modulators of MCH-1 receptor and MCH-mediated ERK signaling. (c) 2009 John Wiley & Sons, Ltd.