Choong Je Ma

Meso-dihydroguaiaretic acid and licarin A of Machilus thunbergii protect against glutamate-induced toxicity in primary cultures of a rat cortical cells

We previously reported that four lignans isolated from the bark of Machilus thunbergii Sieb. et Zucc. (Lauraceae) protected primary cultures of rat cortical neurons from neurotoxicity induced by glutamate. Among the lignans, meso‐dihydroguaiarectic acid (MDGA) and licarin A significantly attenuated glutamate‐induced neurotoxicity when added prior to or right after the excitotoxic glutamate challenge. The neuroprotective activities of two lignans appeared to be more effective in protecting neurons against neurotoxicity induced by NMDA than that induced by kainic acid. MDGA and licarin A diminished the calcium influx that routinely accompanies with the glutamate‐induced neurotoxicity, and inhibited the subsequent overproduction of cellular nitric oxide and peroxide to the level of control cells. They also preserved cellular activities of antioxidative enzymes such as superoxide dismutase, glutathione peroxidase and glutathione reductase reduced in the glutamate‐injured neuronal cells. Thus, our results suggest that MDGA and licarin A significantly protect primary cultured neuronal cells against glutamate‐induced oxidative stress, via antioxidative activities.

Iridoids from Scrophularia buergeriana attenuate glutamate-induced neurotoxicity in rat cortical cultures

In previous work, we isolated 7 neuroprotective iridoid glycosides from the 90% MeOH fraction of Scrophularia buergeriana (Scrophulariaceae). We therefore investigated the mode of action of 8‐O‐E‐p‐methoxycinnamoyl‐harpagide (8‐MCA‐Harp), the most potent neuroprotective iridoid, and its aglycone, harpagide (Harp) using primary cultures of rat cortical cells in vitro. 8‐MCA‐Harp only revealed its neuroprotective activity in a pretreatment paradigm; this iridoid had more selectivity in protecting neurons against N‐methyl‐D‐aspartate (NMDA)‐induced neurotoxicity as opposed to that induced by kainic acid (KA). On the other hand, Harp exerted significant neuroprotective activity when it was administered either before or after glutamate insult and protected cultured neuronal cells from neurotoxicity induced by NMDA or KA. Furthermore, Harp significantly prevented the decrease of glutathione, an antioxidative compound in the brain, in our cultures. Finally, 8‐MCA‐Harp and Harp could successfully reduce the overproduction of nitric oxide and the level of cellular peroxide in cultured neurons. Collectively, these results suggested that Harp and 8‐MCA‐Harp protected primary cultured neurons against glutamate‐induced oxidative stress primarily by acting on the antioxidative defense system and on glutamatergic receptors, respectively.

Calpain inhibitory flavonoids isolated from Orostachys japonicus

The n-butanol (n-BuOH) fraction of Orostachys japonicus A. Berger (Crassulaceae) significantly inhibited calpain activity. Through the activity-guided isolation from the n-BuOH fraction, herbacetin 8-O-α-D-ribopyranoside (1), kaempferol (2), quercetin (3), afzelin (4), astragalin (5), isoquercetin (6) and quercitrin (7) were obtained. Their structures were determined by spectroscopic techniques. Among them, compound 3 and 5 had significant calpain inhibitory activities.

Persicarin from water dropwort (Oenanthe javanica) protects primary cultured rat cortical cells from glutamate‐induced neurotoxicity

The n‐BuOH fraction of O. javanica significantly protected the primary cultures of rat cortical cells exposed to glutamate. Four flavonoids yielded from this fraction through bioactivity‐guidance. The isolated compounds, identified as isorhamnetin (1), afzelin (2), hyperoside (3) and persicarin (4), were evaluated in vitro for their neuroprotective activity. Persicarin (4), the main constituent of O. javanica, showed significant neuroprotective activities in glutamate‐injured rat cortical cells. Persicarin diminished calcium influx and inhibited the subsequent overproduction of nitric oxide and intracellular peroxide. In addition, persicarin significantly restored the reduced activities of glutathione (GSH) reductase and glutathione peroxidase, and the contents of GSH induced by glutamate. These results support a conclusion that persicarin greatly contributes to the neuroprotective activities of O. javanica. Copyright

meso-Dihydroguaiaretic acid attenuates the neurotoxic effect of staurosporine in primary rat cortical cultures

The effect of meso-dihydroguaiaretic acid (MDGA) on the staurosporine-induced neuronal apoptosis and its potential mechanism were investigated using primary cultures of rat cortical cells as an assay system. Treatment of MDGA at the concentrations of 0.1, 1.0 and 10 microM significantly protected neuronal cells against Staurosporine-induced apoptosis. The neuroprotective activity of MDGA was the most potent at the concentration of 1.0 microM and was not increased at higher concentration. MDGA reduced apoptotic characteristics induced by STS; MDGA reduced the condensed nuclei in staurosporine-injured rat cortical cells. MDGA diminished the calcium influx that accompanies the staurosporine-induced apoptosis, and inhibited the subsequent overproduction of reactive oxygen species and peroxide to the level of control cells. It also preserved cellular activity of superoxide dismutase, an antioxidative enzyme reduced by staurosporine insult. In addition, MDGA significantly inhibited caspase-3/7 activation and cytochrome c release. Taken together, these results suggested that MDGA protected neuronal cells against staurosporine-induced apoptosis through the inhibition of Ca(2+) influx, cellular oxidation, cytochrome c release and caspase-3/7 activation.