Jianhui Rong

Potential roles of PI3K/Akt and Nrf2-Keap1 pathways in regulating hormesis of Z-ligustilide in PC12 cells against oxygen and glucose deprivation

Many phytochemicals may ameliorate neurological disorders through a hormetic mechanism. The aim of this study was to characterize the hormetic role of Z-ligustilide in PC12 cells against oxygen glucose deprivation (OGD) induced cell death. We examined the interactions of Z-ligustilide with the pro-survival signals mediated by phosphatidylinositol 3-kinase (PI3K) and transcription factor nuclear factor-erythroid 2 p45-related factor 2 (Nrf2) pathways. We also investigated the effect of Z-ligustilide on the intracellular redox signaling system involving reactive oxygen species (ROS) and glutathione (GSH). Z-ligustilide not only triggered stress response by causing ROS formation and transient GSH depletion, but also activated survival-promoting signals via cross-talking of PI3K and Nrf2 pathways. A key finding was that Z-ligustilide preconditioning protected PC12 cells from OGD-induced injury either at a low concentration for a prolonged period of time or at a high concentration for a short period of time. Presumably, mild preconditioning stimulated moderate ROS production, but effectively activated hormetic signals and induced stress responsive genes. In contrast, higher concentrations of Z-ligustilide could be toxic over a prolonged period of time due to massive ROS production. These results suggest that the effect of Z-ligustilide may be regulated by a biphasic hormetic mechanism involving initial induction of oxidative stress and subsequent activation of stress response gene expression.

Senkyunolides reduce hydrogen peroxide-induced oxidative damage in human liver HepG2 cells via induction of heme oxygenase-1

Rhizoma Chuanxiong is widely used as folk medicine to treat the diseases caused by oxidative stress and inflammation. To delineate the underlying molecular mechanisms, we recently found that Rhizoma Chuanxiong extract significantly induced heme oxygenase-1 (HO-1), an enzyme that degrades intracellular heme into three bioactive products: biliverdin, carbon monoxide and free iron. The anti-inflammatory, antiapoptotic and antiproliferative actions of these products highlight HO-1 as a key endogenous antioxidant and cytoprotective gene. This study was designed to further characterize HO-1 induction of Rhizoma Chuanxiong through bioactivity-guided fractionation. All isolated fractions were assayed for HO-1 induction in human HepG2 cell line at mRNA and protein levels. Based on chromatographic profiling, nuclear magnetic resonance (NMR) and mass spectrometric analysis, the active compounds were identified as senkyunolide-H and its stereoisomer senkyunolide-I. Both senkyunolide isomers inhibited the formation of reactive oxygen species and lipid peroxidation and enhanced the cellular resistance to hydrogen peroxide-induced oxidative damage. Notably, heme oxygenase inhibitor tin protoporphyrin IX (SnPP) significantly suppressed the antioxidant activity of senkyunolide stereoisomers. Thus, this study demonstrated that senkyunolide-H and -I attenuated oxidative damage via activation of HO-1 pathway.

Unexpected neuronal protection of SU5416 against 1- methyl-4-phenylpyridinium ion-induced toxicity via inhibiting neuronal nitric oxide synthase

SU5416 was originally designed as a potent and selective inhibitor of vascular endothelial growth factor receptor-2 (VEGFR-2) for cancer therapy. In this study, we have found for the first time that SU5416 unexpectedly prevented 1-methyl-4-phenylpyridinium ion (MPP+)-induced neuronal apoptosis in cerebellar granule neurons, and decreased 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced loss of dopaminergic neurons and impairment of swimming behavior in zebrafish in a concentration-dependent manner. However, VEGFR-2 kinase inhibitor II, another specific VEGFR-2 inhibitor, failed to reverse neurotoxicity at the concentration exhibiting anti-angiogenic activity, strongly suggesting that the neuroprotective effect of SU5416 is independent from its anti-angiogenic action. SU5416 potently reversed MPP+-increased intracellular nitric oxide level with an efficacy similar to 7-nitroindazole, a specific neuronal nitric oxide synthase (nNOS) inhibitor. Western blotting analysis showed that SU5416 reduced the elevation of nNOS protein expression induced by MPP+. Furthermore, SU5416 directly inhibited the enzyme activity of rat cerebellum nNOS with an IC50 value of 22.7 µM. In addition, knock-down of nNOS expression using short hairpin RNA (shRNA) abolished the neuroprotective effects of SU5416 against MPP+-induced neuronal loss. Our results strongly demonstrate that SU5416 might exert its unexpected neuroprotective effects by concurrently reducing nNOS protein expression and directly inhibiting nNOS enzyme activity. In view of the capability of SU5416 to cross the blood-brain barrier and the safety for human use, our findings further indicate that SU5416 might be a novel drug candidate for neurodegenerative disorders, particularly those associated with NO-mediated neurotoxicity.

The anti-cancer agent SU4312 unexpectedly protects against MPP(+) -induced neurotoxicity via selective and direct inhibition of neuronal NOS.

SU4312, a potent and selective inhibitor of VEGF receptor‐2 (VEGFR‐2), has been designed to treat cancer. Recent studies have suggested that SU4312 can also be useful in treating neurodegenerative disorders. In this study, we assessed neuroprotection by SU4312 against 1‐methyl‐4‐phenylpyridinium ion (MPP+)‐induced neurotoxicity and further explored the underlying mechanisms.

PI3-K/Akt and ERK pathways activated by VEGF play opposite roles in MPP+-induced neuronal apoptosis.

Vascular endothelial growth factor (VEGF), a specific pro-angiogenic peptide, has shown neuroprotective effects in the Parkinsons disease (PD) models, but the underlying mechanisms remain elusive. In this study, the neuroprotective properties of VEGF on 1-methyl-4-phenylpyridinium ion (MPP(+))-induced neurotoxicity in primary cerebellar granule neurons were investigated. Pretreatment of VEGF prevented MPP(+)-induced neuronal apoptosis in a concentration- and time-dependent manner. And this prevention was blocked by PTK787/ZK222584, a VEGF receptor-2 specific inhibitor. Both inhibition of the Akt pathway and activation of the extracellular signal-regulated kinase (ERK) pathway contribute to MPP(+)-induced neuronal apoptosis. VEGF reversed the inhibition of phosphoinositide 3-kinase (PI3-K)/Akt pathway caused by MPP(+), but further enhanced the activation of ERK induced by MPP(+). Interestingly, VEGF and PD98059 (an ERK kinase inhibitor) play a synergistic role in protecting neurons from MPP(+)-induced toxicity. Collectively, these findings suggest that the PI3-K/Akt and ERK pathways activated by VEGF play opposite roles in MPP(+)-induced neuronal apoptosis. This finding offers not only a new and clinically significant modality as to how VEGF exerts its neuroprotective effects but also a novel therapeutic strategy for PD by differentially regulating PD-associated signaling pathways.

Sunitinib Produces Neuroprotective Effect Via Inhibiting Nitric Oxide Overproduction

Sunitinib is an inhibitor of the multiple receptor tyrosine kinases (RTKs) for cancer therapy. Some sunitinib analogues could prevent neuronal death induced by various neurotoxins. However, the neuroprotective effects of sunitinib have not been reported.

Preventing H2O2-induced apoptosis in cerebellar granule neurons by regulating the VEGFR-2/Akt signaling pathway using a novel dimeric antiacetylcholinesterase bis(12)-hupyridone

Oxidative stress-induced apoptosis plays a critical role in the pathogenesis of various neurodegenerative disorders. In this study, the neuroprotective properties of bis(12)-hupyridone (B12H), a novel dimeric acetylcholinesterase (AChE) inhibitor modified from a naturally occurring monomeric analogue, huperzine A, on H₂O₂-induced neurotoxicity were investigated in cerebellar granule neurons (CGNs). Exposure of CGNs to H₂O₂ resulted in apoptosis which could be attenuated by the pre-treatment of B12H (0.3-5 nM) in a concentration-dependent manner. Moreover, tacrine and neostigmine failed to prevent neurotoxicity, indicating that the neuroprotection of B12H might not be due to its inhibitory property of AChE enzymatic activity. Increased activation of extracellular signal-regulated kinase (ERK) and decreased activation of glycogen synthase kinase (GSK) 3β were observed after H₂O₂ exposure, and B12H reversed the altered activation of GSK3β, but not that of ERK. Furthermore, using vascular endothelial growth factor (VEGF), phospho-VEGF receptor-2 (VEGFR-2) antibody, a specific VEGFR-2 inhibitor (PTK787/ZK222584) and specific phosphoinositide 3-kinase inhibitors (LY294002 and wortmannin), it was found that VEGF prevented H₂O₂-induced neuronal loss from activating the VEGF/VEGFR-2 system and that the observed B12H neuroprotective effects might share the same signaling pathway. These findings strongly suggest that B12H prevents H₂O₂-induced neuronal apoptosis independent of inhibiting AChE, but through regulating VEGFR-2/Akt/GSK3β signaling pathway.

Botanical drug puerarin coordinates with nerve growth factor in the regulation of neuronal survival and neuritogenesis via activating ERK1/2 and PI3K/Akt signaling pathways in the neurite extension process.

Nerve growth factor (NGF) regulates neuronal survival and differentiation by activating extracellular signal‐regulated‐kinases (ERK) 1/2 and phosphoinositide‐3‐kinase (PI3K)/Akt pathways in two distinct processes: latency process and neurite extension process. This study was designed to investigate whether botanical drug C‐glucosylated isoflavone puerarin coordinates with NGF to regulate neuritogenesis via activating ERK1/2 and PI3K/Akt in neurite extension process.

Proteomic identification of calcium-binding chaperone calreticulin as a potential mediator for the neuroprotective and neuritogenic activities of fruit-derived glycoside amygdalin

Amygdalin is a fruit-derived glycoside with the potential for treating neurodegenerative diseases. This study was designed to identify the neuroprotective and neuritogenic activities of amygdalin. We initially demonstrated that amygdalin enhanced nerve growth factor (NGF)-induced neuritogenesis and attenuated 6-hydroxydopamine (6-OHDA)-induced neurotoxicity in rat dopaminergic PC12 cells. To define protein targets for amygdalin, we selected a total of 11 mostly regulated protein spots from two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels for protein identification by matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry. We verified the effect of amygdalin on six representative proteins (i.e., calreticulin, Hsp90β, Grp94, 14-3-3η, 14-3-3ζ/δ and Rab GDI-α) for biological relevance to neuronal survival and differentiation. Calcium-binding chaperone calreticulin is of special interest for its activities to promote folding, oligomeric assembly and quality control of proteins that modulate cell survival and differentiation. We transiently knocked down calreticulin expression by specific siRNA and studied its effect on the neuroprotective and neuritogenic activities of amygdalin. We found that amygdalin failed to enhance NGF-induced neuritogenesis in calreticulin-siRNA transfected cells. On the other hand, amygdalin rescued 6-OHDA-induced loss of calreticulin expression. We also found that amygdalin increased the intracellular calcium concentration possibly via inducing calreticulin. Collectively, our results demonstrated the role of calreticulin in mediating the neuroprotective and neuritogenic activities of amygdalin.

Bis(12)-hupyridone, a novel acetylcholinesterase inhibitor, protects against glutamate-induced neuronal excitotoxicity via activating α7 nicotinic acetylcholine receptor/phosphoinositide 3-kinase/Akt cascade.

Bis(12)-hupyridone (B12H), derived from the Chinese medicinal component huperzine A, was originally designed as a novel acetylcholinesterase (AChE) inhibitor. In this paper, we report that B12H (24-h pretreatment) effectively blocked glutamate-induced neuronal excitotoxicity in cerebellar granule neurons (CGNs). However, the huge discrepancy between the EC50 value and IC50 value of B12H, to protect against neuronal toxicity (0.09 μM) and to block the NMDA receptor (21.8 μM) respectively, suggests that the neuroprotection of B12H might be not primarily due to the blockade of the NMDA receptor. Pretreatment by specific antagonists of alpha7-nicotinic acetylcholine receptor (α7nAChR), but not muscarinic acetylcholine receptor (mAChR) or α4β2nAChR, decreased the neuroprotection of B12H. The neuroprotection of B12H could also be abolished by the pretreatment of specific PI3-K inhibitors. Furthermore, B12H restored the suppressed activation of the Akt pathway caused by glutamate as evidenced by the decreased expressions of pSer473-Akt and pSer9-GSK3β. All these results suggest that B12H substantially protected CGNs against glutamate-induced neuronal excitotoxicity via activating α7nAChR/PI3-K/Akt cascade.