Calofolic Acid-A from Calophyllum scriblitifolium Bark Has Vasorelaxant Activity via Indirect PKA Activation Caused by PI-3 Kinase Inhibition in Rat Vascular Smooth Muscle Cells.

Previously, we isolated 2R,3S,15R-calofolic acids (CAs) from Calophyllum scriblitifolium bark, which showed vasorelaxant activity on phenylephrine (PE)-precontracted rat aortic rings. Although the effect was suggested to be induced via an extracellular Ca2+-independent manner and mainly acts on vascular smooth muscle, the exact mechanism of action of CAs remained unclear. Thus, this study investigated the detailed mechanism of calofolic acid-A (CA-A) induced vasorelaxation in an aortic ring specimen using rat vascular smooth muscle cells (VSMCs). The levels of PE-induced phosphorylation on MLC Ser19 decreased in VSMCs pretreated with CA-A. CA-A also decreased the phosphorylation of MYPT1 Thr696 and MYPT1 Thr853. On the other hand, CA-A increased the PE-induced phosphorylation of MYPT1 Ser695 and MYPT1 Ser668, which are reported to be phosphorylated by a cAMP-dependent protein kinase (PKA). CA-A slightly increased PKA substrate phosphorylation in a concentration-dependent manner. Furthermore, CA-A enhanced isoproterenol (ISO)-induced cAMP accumulation and PKA substrate phosphorylation. Treatment with PI-3 kinase (PI3K) inhibitor, LY294002, enhanced ISO-induced cAMP accumulation and PKA substrate phosphorylation in the same manner as CA-A treatment. Furthermore, CA-A was found to directly inhibit PI3K enzyme activity in a dose-dependent manner. Taken together, the present study indicated that CA-A induces vasorelaxation through an indirectly activated PKA-MYPT1 pathway caused by inhibition of PI3K activity.

Cyclolinopeptide F, a cyclic peptide from flaxseed inhibited RANKL-induced osteoclastogenesis via downergulation of RANK expression.

Previously, we reported that cyclolinopeptides (CLs) extracted from flaxseed inhibited receptor activator of nuclear factor κ-B ligand (RANKL)-induced osteoclastogenesis from mouse bone marrow cells in vitro. However, mode of action involved in CLs-inhibited osteoclastogenesis has been yet unknown. Therefore, in this study, we investigated the details of inhibitory activity of cyclolinopeptide-F (CL-F) in osteoclastogenesis, as a representative of CLs. CL-F dose-dependently inhibited RANKL-induced osteoclastogenesis (IC50 0.58 µM) without cytotoxic effects. The inhibition by CL-F was mainly observed in macrophage colony-stimulating factor (M-CSF)-induced proliferation/differentiation phase from M-CSF responsive immature myeloid cells to monocyte/macrophage (M/Mϕ) lineage. Additionally, CL-F also slightly inhibited RANKL-induced differentiation phase from M/Mϕ to mature osteoclasts. Expression of RANKL receptor, RANK, in M-CSF-induced M/Mϕ, i.e. osteoclast progenitor cells, was decreased by CL-F treatment. Furthermore, RT-PCR analysis revealed that CL-F inhibited c-fos gene expression, which is reported to be crucial for RANK expression in osteoclast progenitor cells induced with M-CSF from myeloid lineage cells. These results suggested that CL-F inhibits osteoclastogenesis via down regulation of c-fos expression, which leads to the down-regulation of RANK expression in M-CSF-induced osteoclast progenitors.