Ming-Huan Chan

Differential inhibitory effects of honokiol and magnolol on excitatory amino acid-evoked cation signals and NMDA-induced seizures

The effects of honokiol and magnolol, two major bioactive constituents of the bark of Magnolia officinalis, on Ca(2+) and Na(+) influx induced by various stimulants were investigated in cultured rat cerebellar granule cells by single-cell fura-2 or SBFI microfluorimetry. Honokiol and magnolol blocked the glutamate- and KCl-evoked Ca(2+) influx with similar potency and efficacy, but did not affect KCl-evoked Na(+) influx. However, honokiol was more specific for blocking NMDA-induced Ca(2+) influx, whereas magnolol influenced with both NMDA- and non-NMDA activated Ca(2+) and Na(+) influx. Moreover, the anti-convulsant effects of these two compounds on NMDA-induced seizures were also evaluated. After honokiol or magnolol (1 and 5 mg/kg, i.p.) pretreatment, the seizure thresholds of NMRI mice were determined by tail-vein infusion of NMDA (10 mg/ml). Data showed that both honokiol and magnolol significantly increased the NMDA-induced seizure thresholds, and honokiol was more potent than magnolol. These results demonstrated that magnolol and honokiol have differential effects on NMDA and non-NMDA receptors, suggesting that the distinct therapeutic applications of these two compounds for neuroprotection should be considered.

Antinociceptive actions of honokiol and magnolol on glutamatergic and inflammatory pain

The antinociceptive effects of honokiol and magnolol, two major bioactive constituents of the bark of Magnolia officinalis, were investigated on animal paw licking responses and thermal hyperalgesia induced by glutamate receptor agonists including glutamate, N-methyl-D-aspartate (NMDA), and metabotropic glutamate 5 receptor (mGluR5) activator (RS)-2-chloro-5-hydroxyphenylglycine (CHPG), as well as inflammatory mediators such as substance P and prostaglandin E2 (PGE2) in mice. The actions of honokiol and magnolol on glutamate-induced c-Fos expression in the spinal cord dorsal horn were also examined. Our data showed that honokiol and magnolol blocked glutamate-, substance P- and PGE2-induced inflammatory pain with similar potency and efficacy. Consistently, honokiol and magnolol significantly decreased glutamate-induced c-Fos protein expression in superficial (I-II) laminae of the L4-L5 lumbar dorsal horn. However, honokiol was more selective than magnolol for inhibition of NMDA-induced licking behavioral and thermal hyperalgesia. In contrast, magnolol was more potent to block CHPG-mediated thermal hyperalgesia. These results demonstrate that honokiol and magnolol effectively decreased the inflammatory pain. Furthermore, their different potency on inhibition of nociception provoked by NMDA receptor and mGluR5 activation should be considered.

A gene delivery system for insect cells mediated by arginine-rich cell-penetrating peptides.

Most bioactive macromolecules, such as protein, DNA and RNA, basically cannot permeate into cells freely from outside the plasma membrane. Cell-penetrating peptides (CPPs) are a group of short peptides that possess the ability to traverse the cell membrane and have been considered as candidates for mediating gene and drug delivery into living cells. In this study, we demonstrate that three arginine-rich CPPs (SR9, HR9 and PR9) are able to form stable complexes with plasmid DNA and deliver DNA into insect Sf9 cells in a noncovalent manner. The transferred plasmid DNA containing enhanced green fluorescent protein (EGFP) and red fluorescent protein (RFP) coding regions could be expressed in cells functionally assayed at both the protein and RNA levels. Furthermore, treatment of cells with CPPs and CPP/DNA complexes resulted in a viability of 84-93% indicating these CPPs are not cytotoxic. These results suggest that arginine-rich CPPs appear to be a promising tool for insect transgenesis.

Sarcosine attenuates toluene-induced motor incoordination, memory impairment, and hypothermia but not brain stimulation reward enhancement in mice.

Toluene, a widely used and commonly abused organic solvent, produces various behavioral disturbances, including motor incoordination and cognitive impairment. Toluene alters the function of a large number of receptors and ion channels. Blockade of N-methyl-d-aspartate (NMDA) receptors has been suggested to play a critical role in toluene-induced behavioral manifestations. The present study determined the effects of various toluene doses on motor coordination, recognition memory, body temperature, and intracranial self-stimulation (ICSS) thresholds in mice. Additionally, the effects of sarcosine on the behavioral and physiological effects induced by toluene were evaluated. Sarcosine may reverse toluene-induced behavioral manifestations by acting as an NMDA receptor co-agonist and by inhibiting the effects of the type I glycine transporter (GlyT1). Mice were treated with toluene alone or combined with sarcosine pretreatment and assessed for rotarod performance, object recognition memory, rectal temperature, and ICSS thresholds. Toluene dose-dependently induced motor incoordination, recognition memory impairment, and hypothermia and lowered ICSS thresholds. Sarcosine pretreatment reversed toluene-induced changes in rotarod performance, novel object recognition, and rectal temperature but not ICSS thresholds. These findings suggest that the sarcosine-induced potentiation of NMDA receptors may reverse motor incoordination, memory impairment, and hypothermia but not the enhancement of brain stimulation reward function associated with toluene exposure. Sarcosine may be a promising compound to prevent acute toluene intoxications by occupational or intentional exposure.

Cellular Internalization of Quantum Dots Mediated by Cell-Penetrating Peptides

Nanomaterials have been utilized in biomedical applications for many years because of their unique properties such as quantum confinement, surface plasmon resonance, and superparamagnetism. These applications are expected to advance diagnosis and therapeutics. Fluorescent nanomaterials, such as quantum dots (QDs), were exalted in biological imaging and tracking, and trended to replace protein-based probes. Our previous investigation indicated that cell- penetrating peptides (CPPs) are a promising delivery system that can translocate materials efficiently in a noncovalent manner. In this study, we demonstrate that arginine-rich CPPs can noncovalently complex with QDs and significantly raise efficiency of cellular entry. We further examined their mechanisms of cellular penetrations, subcellular localizations, and cytotoxicity. Importantly, CPP/QD complexes were not toxic at the level of efficient transduction. Collectively, our study provided an insight that CPPs can facilitate the delivery of nanomaterials into cells. Various compositions of CPPs are a major factor affecting uptake routes and efficiency for drug delivery applications.

Toluene exposure during brain growth spurt and adolescence produces differential effects on N-methyl-d-aspartate receptor-mediated currents in rat hippocampus

Toluene, an industrial organic solvent, is voluntarily inhaled as drug of abuse. Because inhibition of N-methyl-d-aspartate (NMDA) receptors is one of the possible mechanisms underlying developmental neurotoxicity of toluene, the purpose of the present study was to examine the effects of toluene exposure during two major neurodevelopmental stages, brain growth spurt and adolescence, on NMDA receptor-mediated current. Rats were administered with toluene (500 mg/kg, i.p.) or corn oil daily over postnatal days (PN) 4-9 (brain growth spurt) or PN 21-26 (early adolescence). Intracellular electrophysiological recordings employing in CA1 pyramidal neurons in the hippocampal slices were performed during PN 30-38. Toluene exposure during brain growth spurt enhanced NMDA receptor-mediated excitatory postsynaptic currents (EPSCs) by electrical stimulation, but impaired the paired-pulse facilitation and NMDA response by exogenous application of NMDA. Toluene exposure during adolescence resulted in an increase in NMDA receptor-mediated EPSCs and a decrease in exogenous NMDA-induced currents, while lack of any effect on paired-pulse facilitation. These findings suggest that toluene exposure during brain growth spurt and adolescence might result in an increase in synaptic NMDA receptor responsiveness and a decrease in extrasynaptic NMDA receptor responsiveness, while only toluene exposure during brain growth spurt can produce presynaptic modulation in CA1 pyramidal neurons. The functional changes in NMDA receptor-mediated transmission underlying developmental toluene exposure may lead to the neurobehavioral disturbances.