Inhibition of Glutamate Release from Rat Cortical Nerve Terminals by Dehydrocorydaline, an Alkaloid from Corydalis yanhusuo.

Kuan-Ming Chiu,I-Yen Chen,Cheng-Wei Lu,Tzu-Yu Lin,Su-Jane Wang,Ming-Yi Lee

doi:10.3390/molecules27030960

Abstract

Excessive release of glutamate induces excitotoxicity and causes neuronal damage in several neurodegenerative diseases. Natural products have emerged as potential neuroprotective agents for preventing and treating neurological disorders. Dehydrocorydaline (DHC), an active alkaloid compound isolated from Corydalis yanhusuo, possesses neuroprotective capacity. The present study investigated the effect of DHC on glutamate release using a rat brain cortical synaptosome model. Our results indicate that DHC inhibited 4-aminopyridine (4-AP)-evoked glutamate release and elevated intrasynaptosomal calcium levels. The inhibitory effect of DHC on 4-AP-evoked glutamate release was prevented in the presence of the vesicular transporter inhibitor bafilomycin A1 and the N- and P/Q-type Ca2+ channel blocker ω-conotoxin MVIIC but not the intracellular inhibitor of Ca2+ release dantrolene or the mitochondrial Na+/Ca2+ exchanger inhibitor CGP37157. Moreover, the inhibitory effect of DHC on evoked glutamate release was prevented by the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) inhibitor PD98059. Western blotting data in synaptosomes also showed that DHC significantly decreased the level of ERK1/2 phosphorylation and synaptic vesicle-associated protein synapsin I, the main presynaptic target of ERK. Together, these results suggest that DHC inhibits presynaptic glutamate release from cerebrocortical synaptosomes by suppressing presynaptic voltage-dependent Ca2+ entry and the MAPK/ERK/synapsin I signaling pathway.

Highlights

In the mammalian brain, glutamate is the primary excitatory neurotransmitter and is involved in many neurological functions, such as learning, memory, long-term potentiation, and synaptic plasticity [1,2,3]
To investigate the mechanisms involved in the neuroprotection of DHC (Figure 1A), we evaluated the release of glutamate in synaptosomes depolarized with the K+ channel blocker 4-AP, which destabilizes membrane potential and opens voltage-dependent Ca2+
Using the fluorescent calcium indicator Fura-2-AM, this study demonstrated that the 4-AP-evoked increase in [Ca2+ ]c was reduced by DHC, indicating the inhibitory effect of DHC on glutamate release by decreasing presynaptic Ca2+ influx through voltage-dependent Ca2+ channels (VDCCs)

Summary

Introduction

Glutamate is the primary excitatory neurotransmitter and is involved in many neurological functions, such as learning, memory, long-term potentiation, and synaptic plasticity [1,2,3]. Excessive glutamate release and activation of glutamate receptors, leading to neuronal overstimulation and excitotoxicity, have been implicated in several neurological or neurodegenerative disorders (NDs), such as epilepsy, multiple sclerosis, Alzheimer’s disease (AD), Huntington’s disease (HD), amyotrophic lateral sclerosis (ALS), and Parkinson’s disease (PD) [3,4,5]. Reducing glutamate release from nerve terminals may be essential for neuroprotection. Dehydrocorydaline (DHC), an active alkaloid compound isolated from Corydalis yanhusuo, was originally proven to reduce noradrenaline release from adrenergic nerve terminals [6]. DHC decreases the production of proinflammatory cytokines and possesses anti-inflammatory effects. DHC can change the content of monoamines in the brain to process antidepressant-like effects [13]. The neuroprotective effects of DHC are still unknown

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