木樨草素在GABAA受體次單位上的調控對相關腦神經抑制功能及氣道黏液過度產生之影響

• Main Authors: Mei-Lin Shen, 沈美伶
• Other Authors: Shung-Te Kao
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/xry8me

博士 === 中國醫藥大學 === 中醫學系博士班 === 104 === Airway mucus overproduction is one of the most common symptoms of asthma that causes severe clinical outcomes in patients. Despite the effectiveness of general asthma therapies, specific treatments that prevent mucus overproduction in asthma patients remain lacking. Recent studies have found that activation of a type GABA receptors (GABAAR) is important for promoting mucus oversecretion in lung airway epithelia. Here, we report that luteolin, a natural flavonoid compound, suppresses mucus overproduction by functionally inhibiting the GABAergic system. This hypothesis was investigated by testing the effects of luteolin on goblet cell hyperplasia, excessive mucus secretion, and GABAergic transmission using histological and electrophysiological approaches. Modulation of the GABAAR is one of the major drug targets for neurological and psychological diseases. The natural flavonoid compound luteolin has been reported to have antidepressant, antinociceptive, and anxiolytic-like effects, which possibly involve the mechanisms of modulating GABA signaling. For example, studies have shown that luteolin has antidepressant and analgesic effects that are considered to be mediated by enhancing GABAAR functions. Furthermore, luteolin has been reported to enhance learning and memory in a neurodegenerative model. However, detailed studies that examine pharmacological effects of luteolin on GABAAR functions are still lacking. We speculated that luteolin might have varied effects on different subtypes of GABAARs to achieve complex neuropharmacological influences. Thus, we also investigated the effects of luteolin on recombinant and endogenous GABAAR-mediated current responses by electrophysiological approaches. Our results showed that 10mg/kg luteolin significantly decreased the number of goblet cells in the lung tissue and inhibited mucus overproduction in an in vivo asthma model induced by ovalbumin (OVA) in mice. Patch-clamp recordings showed that luteolin directly inhibited GABAAR-mediated currents in A549 cells. Furthermore, the inhibitory effects of luteolin on OVA-induced goblet cell hyperplasia and mucus overproduction were occluded by the GABAAR antagonist picrotoxin. These results showed that our observations indicate that luteolin effectively attenuates mucus overproduction at least partially by inhibiting GABAARs. Additionaly, patch-clamp recordings on recombinant and endogenous GABAAR response is showed that luteolin inhibited GABA-mediated currents and slowed the activation kinetics of recombinant α1β2, α1β2γ2, α5β2, and α5β2γ2 receptors with different potency and efficacy. The modulatory effect of luteolin was likely dependent on the subunit composition of the receptor complex: the αβ receptors were more sensitive than the αβγ receptors. In hippocampal pyramidal neurons, luteolin significantly reduced the amplitude and slowed the rise time of miniature postsynaptic currents (mIPSCs). However, GABAAR-mediated tonic currents were not significantly influenced by luteolin. These data suggest that luteolin had negative modulatory effects on both recombinant and endogenous GABAARs and inhibited phasic rather than tonic inhibition in hippocampus. In conclusion, our observations indicate that luteolin effectively attenuates mucus overproduction at least partially by inhibiting GABAARs, suggesting the potential for therapeutic administration of luteolin in the treatment of mucus overproduction in asthma patients.