New and known iridoid- and phenylethanoid glycosides from Harpagophytum procumbens and their in vitro inhibition of human leukocyte elastase.

Ten compounds, harpagoside (1), 8- p-coumaroylharpagide (2), 8-feruloylharpagide (3), 8-cinnamoylmyoporoside (4), pagoside (5), acteoside (6), isoacteoside (7), 6'- O-acetylacteoside (8), cinnamic acid (9) and caffeic acid (10) were isolated from the storage roots of Harpagophytum procumbens, Pedaliaceae. Compounds 1, 2, 6, 7 and 9 are known for H. procumbens; 3 and 10 were isolated the first time from H. procumbens; compounds 4, 5 and 8 are new natural products. Their structures were elucidated using spectroscopic data (NMR, with NOE, COSY and HMBC experiments, UV, [alpha]). The inhibitory activity of aqueous extracts of the roots of H. procumbens and H. zeyheri as well as the main compounds isolated from H. procumbens was tested on human neutrophile elastase. Although inhibition was comparatively weak a dose-dependence was observed. An IC (50) of 542 microg/mL was determined for the aqueous extract of H. procumbens, but 1012 microg/mL for that of H. zeyheri. 6'- O-Acetylacteoside (8), that is not present in H. zeyheri, inhibited the enzyme with an IC (50) of 47 microg/mL (70 microM), compound 7 with 179 microg/mL (286 microM), 2 with 179 microg/mL (331 microM), 5 with 154 microg/mL (260 microM) and 10, which was also used as reference compound, with an IC (50) of 86 microg/mL (475 microM). The IC (50) values of acteoside, harpagoside, cinnamic acid and stachyose were higher than 300 microg/mL and thus not further determined.

In vitro studies indicate that miquelianin (quercetin 3-O-beta-D-glucuronopyranoside) is able to reach the CNS from the small intestine.

Miquelianin (quercetin 3-O-beta-D-glucuronopyranoside) is one of the flavonoids of St. John's wort (Hypericum perforatum L.) whose antidepressant activity has been shown by the forced swimming test, an in vivo pharmacological model with rats. However, nothing is known about its ability to reach the CNS after oral administration. We examined the pathway of miquelianin from the small intestine to the central nervous system using three in vitro membrane barrier cell systems. In the Caco-2 cell line, miquelianin showed a higher uptake (1.93 +/- 0.9 pmol x min(-1) x cm(-2)) than hyperoside (quercetin 3-O-beta-D-galactopyranoside; 0.55 +/- 0.18 pmol x min(-1) x cm(-2)) and quercitrin (quercetin 3-O-alpha-L-rhamnopyranoside; 0.22 +/- 0.08 pmol x min(-1) x cm(-2)). The permeability coefficient of miquelianin (Pc = 0.4 +/- 0.19 x 10(-6) cm/sec) was in the range of orally available drugs assuming sufficient absorption from the small intestine. Uptake and permeability of the examined compounds was increased by the MRP-2 inhibitor MK-571 indicating a backwards transport by this membrane protein. Porcine cell cultures of brain capillary endothelial cells were used as a model of the blood-brain barrier (bbb) and epithelial cells of the plexus chorioidei as a model of the blood-CSF barrier (bcb). Results indicate no active transport in one direction. Although moderate, the permeability coefficients (bbb: Pc = 1.34 +/- 0.05 x 10(-6) cm/sec; bcb: Pc = 2.0 +/- 0.33 x 10(-6) cm/sec) indicate the ability of miquelianin to cross both barriers to finally reach the CNS.