Curcuminoids promote neurite outgrowth in PC12 cells through MAPK/ERK- and PKC-dependent pathways

Lipopolysaccharide and Curcumin Co-Stimulation Potentiates Olfactory Ensheathing Cell Phagocytosis Via Enhancing Their Activation

The gradual deterioration following central nervous system (CNS) injuries or neurodegenerative disorders is usually accompanied by infiltration of degenerated and apoptotic neural tissue debris. A rapid and efficient clearance of these deteriorated cell products is of pivotal importance in creating a permissive environment for regeneration of those damaged neurons. Our recent report revealed that the phagocytic activity of olfactory ensheathing cells (OECs) can make a substantial contribution to neuronal growth in such a hostile environment. However, little is known about how to further increase the ability of OECs in phagocytosing deleterious products. Here, we used an in vitro model of primary cells to investigate the effects of lipopolysaccharide (LPS) and curcumin (CCM) co-stimulation on phagocytic activity of OECs and the possible underlying mechanisms. Our results showed that co-stimulation using LPS and CCM can significantly enhance the activation of OECs, displaying a remarkable up-regulation in chemokine (C-X-C motif) ligand 1, chemokine (C-X-C motif) ligand 2, tumor necrosis factor-α, and Toll-like receptor 4, increased OEC proliferative activity, and improved phagocytic capacity compared with normal and LPS- or CCM-treated OECs. More importantly, this potentiated phagocytosis activity greatly facilitated neuronal growth under hostile culture conditions. Moreover, the up-regulation of transglutaminase-2 and phosphatidylserine receptor in OECs activated by LPS and CCM co-stimulation are likely responsible for mechanisms underlying the observed cellular events, because cystamine (a specific inhibitor of transglutaminase-2) and neutrophil elastase (a cleavage enzyme of phosphatidylserine receptor) can effectively abrogate all the positive effects of OECs, including phagocytic capacity and promotive effects on neuronal growth. This study provides an alternative strategy for the repair of traumatic nerve injury and neurologic diseases with the application of OECs in combination with LPS and CCM.

Modulation of cAMP levels by high-fat diet and curcumin and regulatory effects on CD36/FAT scavenger receptor/fatty acids transporter gene expression

Curcumin, a polyphenol from turmeric (Curcuma longa), reduces inflammation, atherosclerosis, and obesity in several animal studies. In Ldlr^-/- mice fed a high-fat diet (HFD), curcumin reduces plasma lipid levels, therefore contributing to a lower accumulation of lipids and to reduced expression of fatty acid transport proteins (CD36/FAT, FABP4/aP2) in peritoneal macrophages. In this study, we analyzed the molecular mechanisms by which curcumin (500, 1000, 1500 mg/kg diet, for 4 months) may influence plasma and tissue lipid levels in Ldlr^-/- mice fed an HFD. In liver, HFD significantly suppressed cAMP levels, and curcumin restored almost normal levels. Similar trends were observed in adipose tissues, but not in brain, skeletal muscle, spleen, and kidney. Treatment with curcumin increased phosphorylation of CREB in liver, what may play a role in regulatory effects of curcumin in lipid homeostasis. In cell lines, curcumin increased the level of cAMP, activated the transcription factor CREB and the human CD36 promoter via a sequence containing a consensus CREB response element. Regulatory effects of HFD and Cur on gene expression were observed in liver, less in skeletal muscle and not in brain. Since the cAMP/protein kinase A (PKA)/CREB pathway plays an important role in lipid homeostasis, energy expenditure, and thermogenesis by increasing lipolysis and fatty acid β-oxidation, an increase in cAMP levels induced by curcumin may contribute to its hypolipidemic and anti-atherosclerotic effects. © 2016 BioFactors, 43(1):42-53, 2017.

Negletein as a neuroprotectant enhances the action of nerve growth factor and induces neurite outgrowth in PC12 cells

Negletein has been shown to have therapeutic potential for inflammation-associated diseases, but its effect on neurite outgrowth is still unknown. The present study showed that negletein alone did not trigger PC12 cells to differentiate and extend neurites. When compared with the cells in the untreated control, a significant (P < 0.05) induction and a higher neurite outgrowth activity was observed when the cells were cotreated with negletein (10 µM) and a low dose of nerve growth factor (NGF; 5 ng/mL). The neurite outgrowth process was blocked by the tyrosine kinase receptor (Trk) inhibitor, K252a, suggesting that the neuritogenic effect was NGF-dependent. Negletein (10 µM) together with NGF (5 ng/mL) enhanced the phosphorylation of extracellular signal-regulated kinases (ERKs), protein kinase B (Akt), and cAMP response element-binding protein (CREB). The growth associated protein-43 (GAP-43) and the NGF level were also upregulated by negletein (10 µM) and a low dose of NGF (5 ng/mL). Negletein at nanomolar concentration also was found to be sufficient to mediate the survival of serum-deprived PC12 cells up to 72 h. Taken together, negletein might be useful as an efficient bioactive compound to protect neurons from cell death and promote neuritogenesis. © 2016 BioFactors, 42(6):591-599, 2016.

Single cell amperometry reveals curcuminoids modulate the release of neurotransmitters during exocytosis from PC12 cells

We used single cell amperometry to examine whether curcumin and bisdemethoxycurcumin (BDMC), substances that are suggested to affect learning and memory, can modulate monoamine release from PC12 cells. Our results indicate both curcumin and BDMC need long-term treatment (72 h in this study) to influence exocytosis effectively. By analyzing the parameters calculated from single exocytosis events, it can be concluded that curcumin and BDMC affect exocytosis through different mechanisms. Curcumin accelerates the event dynamics with no significant change of the monoamine amount released from single exocytotic events, whereas BDMC attenuates the amount from single exocytotic event with no significant change of the event dynamics. This comparison of the effect of curcumin and BDMC on exocytosis at the single cell level brings insight into their different mechanisms, which might lead to different biological actions. The effect of curcumin and BDMC on the opening and closing of the exocytotic fusion pore were also investigated. These results might be helpful for understanding the improvement of learning and memory and the anti-depression properties of curcuminoids.

Polyhydroxycurcuminoids but not curcumin upregulate neprilysin and can be applied to the prevention of Alzheimer's disease

Neprilysin (NEP) is the most important Aβ-degrading enzyme. Its expression level decreases with age and inversely correlated with amyloid accumulation, suggesting its correlation with the late-onset of Alzheimer's disease. Recently, many reports showed that upregulating NEP level is a promising strategy in the prevention and therapy of Alzheimer's disease. Here, we used a sensitive fluorescence-based Aβ digestion assay to screen 25 curcumin analogs for their ability to upregulate NEP activity. To our surprise, four compounds, dihydroxylated curcumin, monohydroxylated demethoxycurcumin, and mono- and di-hydroxylated bisdemethoxycurcumin, increased NEP activity, while curcumin did not. The ability of these polyhydroxycurcuminoids to upregulate NEP was further confirmed by mRNA and protein expression levels in the cell and mouse models. Finally, feeding monohydroxylated demethoxycurcumin (also named demethylcurcumin) or dihydroxylated bisdemethoxycurcumin (also named bisdemethylcurcumin) to APPswe/PS1dE9 double transgenic mice upregulated NEP levels in the brain and reduced Aβ accumulation in the hippocampus and cortex. These polyhydroxycurcuminoids offer hope in the prevention of Alzheimer's disease.

The potential neurotoxicity of emerging tetrabromobisphenol A derivatives based on rat pheochromocytoma cells

Tetrabromobisphenol A (TBBPA) can cause diverse adverse effects including neurotoxicity. Emerging TBBPA derivatives, with high structure similarity to the parent compound, are now being concerned. In this study, the potential neurotoxicities of four TBBPA derivatives and their parent compound were studied by cell viability inhibition in rat pheochromocytoma cells (PC12) and the corresponding molecular mechanisms were investigated. The cellular toxicity was correlated with the chemical hydrophobicity. Tetrabromobisphenol A bis(2-hydroxyethyl ether) (TBBPA-BHEE) exhibited the highest cellular toxicity to PC12 due to its lowest hydrophobicity among these 5 tested compounds. Further experiments showed that TBBPA-BHEE disturbed dopamine (DA) secretion and altered acetylcholinesterase (AChE) enzymatic activity in PC12 cells. The molecular mechanism study indicated that TBBPA-BHEE induced cellular toxicity to PC12 cells through ROS-mediated caspase activation to a large extent, which was partially attenuated by the anti-oxidation of Vitamin E. Moreover, in contrast to TBBPA, the occurrence of TBBPA-BHEE toxicity to PC12 was not attributed to activation of mitogen-activated protein kinases (MAPKs) or thyroid hormone (TH) signaling pathway. These findings suggest TBBPA derivatives, especially TBBPA-BHEE, as potential neurotoxins need urgent attention.

Polyphenol compounds and PKC signaling

BACKGROUND

Naturally occurring polyphenols found in food sources provide huge health benefits. Several polyphenolic compounds are implicated in the prevention of disease states, such as cancer. One of the mechanisms by which polyphenols exert their biological actions is by interfering in the protein kinase C (PKC) signaling pathways. PKC belongs to a superfamily of serine-threonine kinase and are primarily involved in phosphorylation of target proteins controlling activation and inhibition of many cellular processes directly or indirectly.

SCOPE OF REVIEW

Despite the availability of substantial literature data on polyphenols' regulation of PKC, no comprehensive review article is currently available on this subject. This article reviews PKC-polyphenol interactions and its relevance to various disease states. In particular, salient features of polyphenols, PKC, interactions of naturally occurring polyphenols with PKC, and future perspective of research on this subject are discussed.

MAJOR CONCLUSIONS

Some polyphenols exert their antioxidant properties by regulating the transcription of the antioxidant enzyme genes through PKC signaling. Regulation of PKC by polyphenols is isoform dependent. The activation or inhibition of PKC by polyphenols has been found to be dependent on the presence of membrane, Ca(2+) ion, cofactors, cell and tissue types etc. Two polyphenols, curcumin and resveratrol are in clinical trials for the treatment of colon cancer.

GENERAL SIGNIFICANCE

The fact that 74% of the cancer drugs are derived from natural sources, naturally occurring polyphenols or its simple analogs with improved bioavailability may have the potential to be cancer drugs in the future.

Protective Effects of Minor Components of Curcuminoids on Hydrogen Peroxide-Treated Human HaCaT Keratinocytes

Hydrogen peroxide, one of the reactive oxygen species (ROS), can cause intracellular oxidative stress associated with skin aging and/or photoaging. Curcumin, a polyphenol in turmeric, has been reported to exhibit biological activity. In this study, five naturally occurring curcuminoids [curcumin, demethoxycurcumin (DMC), bisdemethoxycurcumin (BDMC), monohydroxy-DMC, and monohydroxy-BDMC] were used to investigate their protective roles against hydrogen peroxide-induced oxidative stress in the immortalized human keratinocyte cell lines (HaCaT cells). These five curcuminoids at 10 μM, but not at 5 μM, were shown to exhibit cytotoxicities toward HaCaT keratinocytes. Therefore, a 5 μM concentration of the five curcuminoids was selected for further investigations. Cells were pretreated with or without curcuminoids for 2.5 h before 24-h hydrogen peroxide (150 μM) treatments. Pretreatments with the minor components monohydroxy-DMC or monohydroxy-BDMC, but not curcumin, DMC, and BDMC, showed protective activity, elevating cell viability compared to cells with direct hydrogen peroxide treatments. Pretreatments with monohydroxy-DMC and monohydroxy-BDMC showed the best protective effects, reducing apoptotic cell populations and intracellular ROS, as demonstrated by flow cytometry, as well as reducing the changes of the mitochondrial membrane potential compared to cells with direct hydrogen peroxide treatments. The pretreatments with monohydroxy-DMC and monohydroxy-BDMC reduced c-jun and c-fos mRNA expression and p53 tumor suppressor protein expression and increased HO-1 protein expression and glutathione peroxidase (GPx) activity, respectively, compared to cells with direct hydrogen peroxide treatments. The five curcuminoids exhibited similar hydrogen peroxide-scavenging activity in vitro. It was proposed that monohydroxy-DMC and monohydroxy-BDMC could induce antioxidant defense systems better than curcumin, DMC, or BDMC could against hydrogen peroxide-induced oxidative stress and apoptosis of HaCaT keratinocytes and that they may have potential as ingredients in antiaging cosmetics for skin care.

Stimulating the proliferation, migration and lamellipodia of Schwann cells using low-dose curcumin

Transplantation of peripheral glia is being trialled for neural repair therapies, and identification of compounds that enhance the activity of glia is therefore of therapeutic interest. We have previously shown that curcumin potently stimulates the activity of olfactory glia. We have now examined the effect of curcumin on Schwann cell (SC) activities including proliferation, migration and the expression of protein markers. SCs were treated with control media and with different concentrations of curcumin (0.02-20 μM). Cell proliferation was determined by MTS assay and migration changes were determined by single live cell migration tracking. We found that small doses of curcumin (40 nM) dramatically increased the proliferation and migration in SCs within just one day. When compared with olfactory glia, curcumin stimulated SC proliferation more rapidly and at lower concentrations. Curcumin significantly increased the migration of SCs, and also increased the dynamic activity of lamellipodial waves which are essential for SC migration. Expression of the activated form of the MAP kinase p38 (p-p38) was significantly decreased in curcumin-treated SCs. These results show that curcumin's effects on SCs differ remarkably to its effects on olfactory glia, suggesting that subtypes of closely related glia can be differentially stimulated by curcumin. Overall these results demonstrate that the therapeutically beneficial activities of glia can be differentially enhanced by curcumin which could be used to improve outcomes of neural repair therapies.

Modulation of neurotrophic signaling pathways by polyphenols

Polyphenols are an important class of phytochemicals, and several lines of evidence have demonstrated their beneficial effects in the context of a number of pathologies including neurodegenerative disorders such as Alzheimer’s and Parkinson’s disease. In this report, we review the studies on the effects of polyphenols on neuronal survival, growth, proliferation and differentiation, and the signaling pathways involved in these neurotrophic actions. Several polyphenols including flavonoids such as baicalein, daidzein, luteolin, and nobiletin as well as nonflavonoid polyphenols such as auraptene, carnosic acid, curcuminoids, and hydroxycinnamic acid derivatives including caffeic acid phentyl ester enhance neuronal survival and promote neurite outgrowth in vitro, a hallmark of neuronal differentiation. Assessment of underlying mechanisms, especially in PC12 neuronal-like cells, reveals that direct agonistic effect on tropomyosin receptor kinase (Trk) receptors, the main receptors of neurotrophic factors including nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) explains the action of few polyphenols such as 7,8-dihydroxyflavone. However, several other polyphenolic compounds activate extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase (PI3K)/Akt pathways. Increased expression of neurotrophic factors in vitro and in vivo is the mechanism of neurotrophic action of flavonoids such as scutellarin, daidzein, genistein, and fisetin, while compounds like apigenin and ferulic acid increase cyclic adenosine monophosphate response element-binding protein (CREB) phosphorylation. Finally, the antioxidant activity of polyphenols reflected in the activation of Nrf2 pathway and the consequent upregulation of detoxification enzymes such as heme oxygenase-1 as well as the contribution of these effects to the neurotrophic activity have also been discussed. In conclusion, a better understanding of the neurotrophic effects of polyphenols and the concomitant modulations of signaling pathways is useful for designing more effective agents for management of neurodegenerative diseases.

Curcuminoids Modulate the PKCδ/NADPH Oxidase/Reactive Oxygen Species Signaling Pathway and Suppress Matrix Invasion during Monocyte-Macrophage Differentiation

Monocyte recruitment and invasion play critical roles in the initiation and progression of atherosclerosis. The reduction in monocyte adhesion and infiltration is thought to exert antiatherosclerotic effects. Curcumin, demethoxycurcumin (DMC), and bisdemethoxycurcumin (BDMC) are the major active components of curcuminoids and exhibit several biological activities, including anti-inflammatory, anticarcinogenic, and hypocholesterolemic activities. The aim of this study was to investigate the antiatherogenic effects and mechanisms of curcuminoids during monocyte to macrophage differentiation. The results showed that curcumin, DMC, and BDMC (20 μM) suppressed matrix invasion from 100.0 ± 5.0% to 24.8 ± 1.4%, 26.6 ± 2.9%, and 33.7 ± 1.7%, respectively, during PMA-induced THP-1 differentiation. We found that curcuminoids significantly reduced PMA-induced CD11b and MMP-9 expression by THP-1 cells. Production of reactive oxygen species (ROS) induced by PMA (126.7 ± 2.1%) was markedly attenuated by curcumin, DMC, and BDMC to 99.5 ± 7.8%, 87.8 ± 8.2%, and 89.8 ± 7.6%, respectively, resulting in the down-regulation of CD11b and MMP-9 expression. We demonstrated that curcuminoids inhibited NADPH oxidase through the down-regulation of NOX2 expression and the reduction of p47phox membrane translocation. Moreover, we found involvement of PKCδ in the PMA-induced NOX2, CD11b, and MMP-9 mRNA expression. Curcumin, DMC, and BDMC decreased the active form of PKCδ protein stimulated by PMA in THP-1 cells. Overall, our results reveal that curcuminoids suppress matrix invasion through the inhibition of the PKCδ/NADPH oxidase/ROS signaling pathway during monocyte-macrophage differentiation.

Absolute Configurations and NO Inhibitory Activities of Terpenoids from Curcuma longa

Curcuma longa L., belonging to the Zingiberaceae family, is a perennial herb and has been used as a spice and a pigment in the food industry. In the ongoing search for inhibitory reagents of NO production and survey of the chemical composition of natural vegetable foods, the chemical constituents of C. longa used as spice were investigated. This investigation resulted in the isolation of 2 new terpenoids and 14 known analogues. Their structures were established on the basis of the extensive analyses of 1D and 2D NMR spectroscopic data, and the absolute configurations of 1-4 were elucidated by comparison of the calculated and experimental ECD spectra. Among them, compound 1 is a rare norditerpene with an ent-labdane skeleton, and 2 is a skeletally novel sesquiterpene having an eight-membered ring. All of the compounds were found to possess NO inhibitory activities in murine microglial BV-2 cells. The discovery of two new compounds in this chemical investigation further disclosed the chemical composition of C. longa used a food spice, and the bioassay implied that the natural food spice C. longa, containing terpenoids with NO inhibitory activities, may be potentially promotive to human health.

Phytochemicals that regulate neurodegenerative disease by targeting neurotrophins: a comprehensive review

Alzheimer's disease (AD), characterized by progressive dementia and deterioration of cognitive function, is an unsolved social and medical problem. Age, nutrition, and toxins are the most common causes of AD. However, currently no credible treatment is available for AD. Traditional herbs and phytochemicals may delay its onset and slow its progression and also allow recovery by targeting multiple pathological causes by antioxidative, anti-inflammatory, and antiamyloidogenic properties. They also regulate mitochondrial stress, apoptotic factors, free radical scavenging system, and neurotrophic factors. Neurotrophins such as BDNF, NGF, NT3, and NT4/5 play a vital role in neuronal and nonneuronal responses to AD. Neurotrophins depletion accelerates the progression of AD and therefore, replacing such neurotrophins may be a potential treatment for neurodegenerative disease. Here, we review the phytochemicals that mediate the signaling pathways involved in neuroprotection specifically neurotrophin-mediated activation of Trk receptors and members of p75(NTR) superfamily. We focus on representative phenolic derivatives, iridoid glycosides, terpenoids, alkaloids, and steroidal saponins as regulators of neurotrophin-mediated neuroprotection. Although these phytochemicals have attracted attention owing to their in vitro neurotrophin potentiating activity, their in vivo and clinical efficacy trials has yet to be established. Therefore, further research is necessary to prove the neuroprotective effects in preclinical models and in humans.

Up-Regulation of miR-34a Expression in Response to the Luteolin-Induced Neurite Outgrowth of PC12 Cells

Luteolin (3',4',5,7-tetrahydroxyflavone), a flavonoid found in several vegetables and fruits, has been reported to possess neurotrophic activities that are associated with its capacity to promote neuronal survival and differentiation. In the present study, we report for the first time a genomewide screen for microRNAs (miRNAs) regulated during the luteolin-mediated neurite outgrowth of PC12 cells. We found that after luteolin treatment, the abundance of 16 miRNAs was markedly up-regulated and that of 3 miRNAs was down-regulated in PC12 cells. The induction of miR-34a by luteolin was the most pronounced among these differentially expressed miRNAs. The correlation between miR-34a down-regulation and decreased luteolin-mediated neurite outgrowth may indicate a mechanism by which miR-34a may act as a modulator of neuronal differentiation. Furthermore, we found that luteolin enhanced the phosphorylation of p53 at Ser15, which was associated with the promotion of miR-34a transcription and neurite outgrowth. Moreover, the level of sirtuin 1 (SIRT1), a known miR-34a target, was reduced during luteolin-induced neurite outgrowth. In turn, the level of acetylated p53, a substrate of SIRT1, was correspondingly increased in luteolin-treated PC12 cells. In addition to p53 activation, we further identified that luteolin-induced miR-34a transcription and neurite outgrowth involved the activation of the JNK and p38 MAPK pathways. However, the inhibition of JNK and p38 MAPK activation did not block luteolin-induced p53 activation in PC12 cells. Our findings suggested that the activation of both p53-dependent and p53-independent miR-34a/SIRT1 pathways plays a critical role in the mechanisms underlying luteolin-induced neuritogenesis.

Demethoxycurcumin modulates human P-glycoprotein function via uncompetitive inhibition of ATPase hydrolysis activity

Curcuminoids are major components of Curcuma longa L., which is widely used as spice in food. This study aimed at identifying whether curcumin, demethoxycurcumin, and bisdemethoxycurcumin could modulate efflux function of human P-glycoprotein and be used as chemosensitizers in cancer treatments. Without altering P-glycoprotein expression levels and conformation, the purified curcuminoids significantly inhibited P-glycoprotein efflux function. In rhodamine 123 efflux and calcein-AM accumulation assays, demethoxycurcumin demonstrated the highest inhibition potency (inhibitory IC50 = 1.56 ± 0.13 μM) among the purified curcuminoids, as well as in the fold of reversal assays. Demethoxycurcumin inhibited P-glycoprotein-mediated ATP hydrolysis under concentrations of <1 μM and efficiently inhibited 200 μM verapamil-stimulated ATPase activity, indicating a high affinity of demethoxycurcumin for P-glycoprotein. These results suggested that demethoxycurcumin may be a potential additive natural product in combination with chemotherapeutic agents in drug-resistant cancers.

Low-dose curcumin stimulates proliferation, migration and phagocytic activity of olfactory ensheathing cells

One of the promising strategies for neural repair therapies is the transplantation of olfactory ensheathing cells (OECs) which are the glial cells of the olfactory system. We evaluated the effects of curcumin on the behaviour of mouse OECs to determine if it could be of use to further enhance the therapeutic potential of OECs. Curcumin, a natural polyphenol compound found in the spice turmeric, is known for its anti-cancer properties at doses over 10 µM, and often at 50 µM, and it exerts its effects on cancer cells in part by activation of MAP kinases. In contrast, we found that low-dose curcumin (0.5 µM) applied to OECs strikingly modulated the dynamic morphology, increased the rate of migration by up to 4-fold, and promoted significant proliferation of the OECs. Most dramatically, low-dose curcumin stimulated a 10-fold increase in the phagocytic activity of OECs. All of these potently stimulated behavioural characteristics of OECs are favourable for neural repair therapies. Importantly, low-dose curcumin gave a transient activation of p38 kinases, which is in contrast to the high dose curcumin effects on cancer cells in which these MAP kinases tend to undergo prolonged activation. Low-dose curcumin mediated effects on OECs demonstrate cell-type specific stimulation of p38 and ERK kinases. These results constitute the first evidence that low-dose curcumin can modulate the behaviour of olfactory glia into a phenotype potentially more favourable for neural repair and thereby improve the therapeutic use of OECs for neural repair therapies.

The effect of the left stellate ganglion on sympathetic neural remodeling of the left atrium in rats following myocardial infarction

BACKGROUND

The neural remodeling of the atrium plays an important role in the initiation of atrial fibrillation after myocardial infarction (MI); however, the effects of the left stellate ganglion (LSG) on the neural remodeling of the atrium remain incompletely understood. Thus, this study investigated the mechanism by which the LSG mediates sympathetic neural remodeling of the left atrium (LA) in rats after MI.

METHODS

Sixty rats were randomly divided into a Sham group and an MI group. The expression levels of growth-associated protein-43 (GAP43) and nerve growth factor (NGF) messenger ribonucleic acid (mRNA) were measured by reverse transcription polymerase chain reaction. Immunohistochemistry was used to detect the distribution and density of GAP43- and NGF-positive nerves. The expression levels of the proteins were quantified by Western blotting.

RESULTS

Compared with the Sham group, GAP43 mRNA expression in the LSG was increased in the MI group (P < 0.01), but not significantly increased in the LA. Immunohistochemical analysis demonstrated that in both the LSG and the LA, the mean densities of GAP43- and NGF-positive nerves in the MI group were increased (P < 0.01). In both the LSG and the LA, the protein levels of GAP43 and NGF in the MI group were increased relative to the Sham group (P < 0.01).

CONCLUSIONS

The increased levels of NGF and GAP43 proteins can induce sympathetic nerve hyperinnervation in the LSG and the LA after MI. The increased GAP43 proteins in the LA, which may have been transported from the LSG, accelerated LA sympathetic neural remodeling in rats.

Can proline-rich polypeptide complex mimic the effect of nerve growth factor?

Naturally occurring compounds that can act as prosurvival factors and neurite formation stimulants in the conditions of reduced neurotrophins production are important both in neuronal protection and therapy of neurodegenerative disorders. Therefore, the role of proline-rich polypeptide complex (PRP) and its nonapeptide fragment (NP) in the promotion of pheochromocytoma cell line (PC12) survival and neurite outgrowth pathway is presented. It was shown that PRP/NP did not affect the neuronal nitric oxide synthase (nNOS) at the transcriptional and protein level. However, the activity of nNOS and intracellular nitric oxide (NO) concentration was markedly increased after treatment of PC12 cells with peptides. This reaction was inhibited by L-NAME-nNOS inhibitor. It was shown that PRP and NP induce the soluble guanylyl cyclase to release higher amount of cyclic GMP (cGMP), and subsequently, the increased phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) is observed. This effect was abolished by both U0126 (inhibitor of ERK1/2) and also by L-NAME. Reduction of ERK1/2 activity observed in the presence of nNOS inhibitor suggests that its activation is NO-dependent. The presented results shed some light on the mechanism of action of PRP complex. PRP and NP can activate NO/cGMP/ERK1/2 signaling pathway, similarly to nerve growth factor (NGF). The prosurvival action and short fibers formation suggest the role of PRP and NP in neuroprotection and the initiation of neuritogenesis. They can also participate in the amplification of signals controlling the survival and differentiation of neurons effect when the deficit of NGF takes place.

Flavonoids, derived from traditional Chinese medicines, show roles in the differentiation of neurons: possible targets in developing health food products

Flavonoids, a family of phenolic compounds, are distributed in a variety of fruits, vegetables, tea, and wine. More importantly, many flavonoids are served as the active ingredients in traditional Chinese herbal medicines, which in general do not have side effects. Several lines of evidence support that flavonoids have impacts on many aspects of human health, including anti-tumor, anti-oxidation, and anti-inflammation. Recently, there is significant attention focused on the neuronal beneficial effects of flavonoids, including the promotion of nervous system development, neuroprotection against neurotoxin stress, as well as the promotion of memory, learning, and cognitive functions. Here, the activities of flavonoids on the development of nervous system are being summarized and discussed. The flavonoids from diverse herbal medicines have significant effects in different developmental stages of nervous systems, including neuronal stem cell differentiation, neurite outgrowth, and neuronal plasticity. These findings imply that flavonoids are potential candidates for the development of health supplements in preventing birth defects and neuronal diseases.

Investigations of curcumin and resveratrol on neurite outgrowth: perspectives on spinal muscular atrophy

Spinal Muscular Atrophy (SMA) is an autosomal recessive neurodegenerative disease with progressive muscle weakness and atrophy. SMA is caused by low levels of the Survival of Motor Neuron (SMN) protein, which also leads to neurite outgrowth defects in neuronal cells. Rescue of the outgrowth defect is thought to be a strategy for SMA treatment. Polyphenolic histone deacetylase (HDAC) inhibitors might be good candidates due to their neuritogenic properties. In the present study, it was investigated whether neurite outgrowth defects could be rescued by curcumin and resveratrol, which are SMN-inducing polyphenols, having HDAC inhibition activity. According to our results, although curcumin and resveratrol failed to restore the neurite outgrowth defects, the SMN protein was found to be necessary for the neurite-promoting activity of curcumin in neuron-like PC12 cells.

Synthesis of caffeic acid phenethyl ester derivatives, and their cytoprotective and neuritogenic activities in PC12 cells

Twenty-one caffeic acid phenethyl ester (CAPE) derivatives were synthesized, and characterized by IR, HR-MS, (1)H and (13)C NMR analyses. All compounds were evaluated for their cytoprotective effects against H2O2-induced cytotoxicity and neuritogenic activities in the neurite outgrowth in PC12 cells. Compounds 1 and 20 exhibited stronger cytoprotective activities than their parent compound CAPE at 4 nM. Compounds 1, 4, 12 and 13 showed potential neuritogenic activities at 0.5 nM, while compounds 19 and 20 induced neurite outgrowth at 10 nM. The results from this study suggested that CAPE and its derivatives may be potential functional food ingredients for the prevention of neurodegenerative diseases.

Global signaling effects of a schizophrenia-associated missense mutation in neuregulin 1: an exploratory study using whole genome and novel kinome approaches

Aberrant neuregulin 1-ErbB4 signaling has been implicated in schizophrenia. We previously identified a novel schizophrenia-associated missense mutation (valine to leucine) in the NRG1 transmembrane domain. This variant inhibits formation of the NRG1 intracellular domain (ICD) and causes decreases in dendrite formation. To assess the global effects of this mutation, we used lymphoblastoid cell lines from unaffected heterozygous carriers (Val/Leu) and non-carriers (Val/Val). Transcriptome data showed 367 genes differentially expressed between the two groups (Val/Val N = 6, Val/Leu N = 5, T test, FDR (1 %), α = 0.05, -log10 p value >1.5). Ingenuity pathway (IPA) analyses showed inflammation and NRG1 signaling as the top pathways altered. Within NRG1 signaling, protein kinase C (PKC)-eta (PRKCH) and non-receptor tyrosine kinase (SRC) were down-regulated in heterozygous carriers. Novel kinome profiling (serine/threonine) was performed after stimulating cells (V/V N = 6, V/L N = 6) with ErbB4, to induce release of the NRG1 ICD, and revealed significant effects of treatment on the phosphorylation of 35 peptides. IPA showed neurite outgrowth (six peptides) as the top annotated function. Phosphorylation of these peptides was significantly decreased in ErbB4-treated Val/Val but not in Val/Leu cells. These results show that perturbing NRG1 ICD formation has major effects on cell signaling, including inflammatory and neurite formation pathways, and may contribute significantly to schizophrenia pathophysiology.

Curcumin-loaded nanoparticles potently induce adult neurogenesis and reverse cognitive deficits in Alzheimer's disease model via canonical Wnt/β-catenin pathway

Neurogenesis, a process of generation of new neurons, is reported to be reduced in several neurodegenerative disorders including Alzheimer's disease (AD). Induction of neurogenesis by targeting endogenous neural stem cells (NSC) could be a promising therapeutic approach to such diseases by influencing the brain self-regenerative capacity. Curcumin, a neuroprotective agent, has poor brain bioavailability. Herein, we report that curcumin-encapsulated PLGA nanoparticles (Cur-PLGA-NPs) potently induce NSC proliferation and neuronal differentiation in vitro and in the hippocampus and subventricular zone of adult rats, as compared to uncoated bulk curcumin. Cur-PLGA-NPs induce neurogenesis by internalization into the hippocampal NSC. Cur-PLGA-NPs significantly increase expression of genes involved in cell proliferation (reelin, nestin, and Pax6) and neuronal differentiation (neurogenin, neuroD1, neuregulin, neuroligin, and Stat3). Curcumin nanoparticles increase neuronal differentiation by activating the Wnt/β-catenin pathway, involved in regulation of neurogenesis. These nanoparticles caused enhanced nuclear translocation of β-catenin, decreased GSK-3β levels, and increased promoter activity of the TCF/LEF and cyclin-D1. Pharmacological and siRNA-mediated genetic inhibition of the Wnt pathway blocked neurogenesis-stimulating effects of curcumin. These nanoparticles reverse learning and memory impairments in an amyloid beta induced rat model of AD-like phenotypes, by inducing neurogenesis. In silico molecular docking studies suggest that curcumin interacts with Wif-1, Dkk, and GSK-3β. These results suggest that curcumin nanoparticles induce adult neurogenesis through activation of the canonical Wnt/β-catenin pathway and may offer a therapeutic approach to treating neurodegenerative diseases such as AD, by enhancing a brain self-repair mechanism.

Curcumin protects axons from degeneration in the setting of local neuroinflammation

Axon degeneration is a hallmark of several central nervous system (CNS) disorders, including multiple sclerosis (MS), Alzheimer's disease (AD) and Parkinson's disease (PD). Previous neuroprotective approaches have mainly focused on reversal or prevention of neuronal cell body degeneration or death. However, experimental evidence suggests that mechanisms of axon degeneration may differ from cell death mechanisms, and that therapeutic agents that protect cell bodies may not protect axons. Moreover, axon degeneration underlies neurologic disability and may, in some cases, represent an important initial step that leads to neuronal death. Here, we develop a novel quantitative microfluidic-based methodology to assess mechanisms of axon degeneration caused by local neuroinflammation. We find that LPS-stimulated microglia release soluble factors that, when applied locally to axons, result in axon degeneration. This local axon degeneration is mediated by microglial MyD88/p38 MAPK signaling and concomitant production of nitric oxide (NO). Intra-axonal mechanisms of degeneration involve JNK phosphorylation. Curcumin, a compound with both anti-oxidant and JNK inhibitory properties, specifically protects axons, but not neuronal cell bodies, from NO-mediated degeneration. Overall, our platform provides mechanistic insights into local axon degeneration, identifies curcumin as a novel axon protectant in the setting of neuroinflammation, and allows for ready screening of axon protective drugs.

Curcumin promotes neurite outgrowth via reggie-1/flotillin-2 in cortical neurons

Curcumin is well known as an antioxidant and anti-inflammatory agent. In this study, we provided convincing evidence for the function of curcumin in neurite outgrowth of cortical neurons. We discovered that curcumin treatment could promote the number of processes, mean process length, and maximum process length of primary neurons, which were inhibited by reggie-1 siRNAs or extracellular signal-regulated kinase (ERK) 1/2 antagonist. Furthermore, curcumin-induced neurite growth was related to the ERK1/2 phosphorylation, which was blocked by reggie-1 knockdown. Overall, our results implied that curcumin could mediate neurite outgrowth through reggie-1 and ERK1/2 pathway.

Neurotrophic action of 5-hydroxylated polymethoxyflavones: 5-demethylnobiletin and gardenin A stimulate neuritogenesis in PC12 cells

Polymethoxyflavones (PMFs) exhibit a broad spectrum of biological properties, including anticancer, antiatherogenic, and neuroprotective effects. The aim of this study is to investigate the neurotrophic effects of 5-demethylnobiletin, a hydroxylated PMF found in citrus plants, and gardenin A, a synthetic PMF analogue, on neurite outgrowth and neuronal differentiation in PC12 cells. The results of this study showed that 5-demethylnobiletin and gardenin A (10-20 μM) potently induce neurite outgrowth in PC12 cells, accompanied by the expression of neuronal differentiation and synapse formation marker proteins, growth-associated protein-43 (GAP-43), and synaptophysin. We observed that the addition of K252a, a TrKA antagonist, significantly inhibited NGF-induced neurite outgrowth in PC12 cells, but 5-demethylnobiletin- or gardenin A-induced neurite outgrowth was not affected. Treatment with 5-demethylnobiletin and gardenin A markedly induced the phosphorylation of both cyclic AMP response element-binding protein (CREB) and CRE-mediated transcription, which was suppressed through the administration of the inhibitor 2-naphthol AS-E phosphate (KG-501) or using CREB siRNA. Furthermore, our results showed that MAPK/ERK kinase 1/2 (MEK1/2), protein kinase A (PKA), and protein kinase C (PKC) inhibitors blocked the CRE transcription activity and neurite outgrowth induced through 5-demethylnobiletin or gardenin A. Consistently, increased ERK phosphorylation and PKA and PKC activities were observed in PC12 cells treated with 5-demethylnobiletin or gardenin A. These results reveal for the first time that 5-demethylnobiletin and gardenin A promote neuritogenesis through the activation of MAPK/ERK-, PKC-, and PKA-dependent, but not TrkA-dependent, CREB signaling pathways in PC12 cells.

Potentiation of neuritogenic activity of medicinal mushrooms in rat pheochromocytoma cells

BACKGROUND

Senescence of the neurons is believed to be a focal factor in the development of age-related neurodegenerative diseases such as Alzheimer's disease. Diminutions in the levels of nerve growth factor (NGF) lead to major declines in brain cell performance. Functional foods, believed to mitigate this deficiency, will be reaching a plateau in the near future market of alternative and preventive medicine. In the search for neuroactive compounds that mimic the NGF activity for the prevention of neurodegenerative diseases, the potential medicinal values of culinary and medicinal mushrooms attract intense interest.

METHODS

Cytotoxic effects of aqueous extracts of three medicinal mushrooms basidiocarps, Ganoderma lucidum, Ganoderma neo-japonicum and Grifola frondosa towards rat pheochromocytoma (PC-12) cells were determined by 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The potentiation of neuritogenic activity was assessed by neurite outgrowth stimulation assay. Involvement of cellular signaling pathways, mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (MEK/ERK1/2) and phosphoinositide-3-kinase/protein kinase B (PI3K/Akt) in mushrooms-stimulated neuritogenesis were examined by using specific pharmacological inhibitors. Alteration of neuronal morphology by inhibitors was visualized by immunofluorescence staining of the neurofilament.

RESULTS

All the aqueous extracts tested caused a marked stimulation of neuritogenesis with no detectable cytotoxic effects towards PC-12 cells. The aqueous extract of G. neo-japonicum triggered maximal stimulation of neurite outgrowth at a lower concentration (50 μg/ml) with 14.22 ± 0.43% of neurite-bearing cells, compared to G. lucidum and G. frondosa that act at a higher concentration (75 μg/ml), with 12.61 ± 0.11% and 12.07 ± 0.46% of neurite-bearing cells, respectively. The activation of MEK/ERK1/2 and PI3K/Akt signaling pathways were necessary for the NGF and aqueous extracts to promote neuritogenesis.

CONCLUSIONS

Ganoderma lucidum, G. neo-japonicum and G. frondosa may contain NGF-like bioactive compound(s) for maintaining and regenerating the neuronal communications network. The present study reports the first evidence of the neuritogenic effects of aqueous extracts of basidiocarps of G. neo-japonicum in-vitro and showed the involvement of MEK/ERK1/2 and P13K/Akt signaling pathways for neuritogenesis in PC-12 cells.

Combination Effects of Curcumin and Aqueous Extract of Lignosus rhinocerotis Mycelium on Neurite Outgrowth Stimulation Activity in PC-12 Cells

Neurotrophic factors are necessary for neuronal navigation to form viable neuronal networks. These factors are high molecular weight polypeptides that cannot cross the blood brain-barrier. Therefore, small molecules from mushrooms and plants are utilized to maintain neuronal function or up-regulate neurotrophic factors. The present study investigated whether a combination of Lignosus rhinocerotis mycelium aqueous extract and curcumin was more effective than L. rhinocerotis mycelium or curcumin alone in the stimulation of neurite outgrowth of PC-12 cells. The maximum neurite extension for L. rhinocerotis and curcumin was at 21.1% at 20 μg/mL and 29.5% at 10 μg/mL, respectively. Combining 20 μg/mL of L. rhinocerotis with one μg/mL curcumin gave 27.2% neurite extension. This combination was preferred because high concentrations of curcumin were toxic to cells. In the combination, 20 μg/mL of L. rhinocerotis enhanced neurite outgrowth activity at a lower dosage of curcumin at one μg/mL, and produced a comparable percentage of neurite outgrowth stimulation activity to L. rhinocerotis and curcumin alone in PC-12 cells.

Capsaicin-induced activation of ERK1/2 and its involvement in GAP-43 expression and CGRP depletion in organotypically cultured DRG neurons

Low concentrations of capsaicin (CAP) stimulate and high concentrations of CAP can be toxic to the primary sensory neurons of the dorsal root ganglion (DRG). CAP induces the phosphorylation of extracellular signal-regulated protein kinases 1/2 (ERK1/2) in DRG neurons. The effect of the activation of ERK1/2 by different concentrations of CAP on growth-associated protein 43 (GAP-43) expression and calcitonin gene-related peptide (CGRP) depletion in DRG neurons remains unknown. In the present study, organotypic embryonic 15-day-old rat DRG explants were used to determine the effect of different concentrations of CAP on GAP-43 expression and CGRP depletion. The results showed that, compared to unstimulated control cultures, GAP-43 and pERK1/2 protein levels increased at a low concentration (2 μmol/L) of CAP and decreased at a higher concentration (10 μmol/L). The number of CGRP-immunoreactive (IR) migrating neurons also decreased in CAP-treated cultures. The increase in GAP-43 levels and CGRP depletion could be blocked by the administration of ERK1/2 inhibitor PD98059. The results of the present study imply that CAP at different concentrations has different effects on GAP-43 expression and CGRP depletion. These effects were involved in the activation of ERK1/2 in organotypically cultured DRG neurons stimulated with CAP. These data may provide new insights for further development potential therapeutic applications of CAP with moderate dose on neurogenic inflammation.

Molecular mechanisms of hypolipidemic effects of curcumin

Recent evidence suggests potential benefits from phytochemicals and micronutrients in reducing the elevated oxidative and lipid-mediated stress associated with inflammation, obesity, and atherosclerosis. These compounds may either directly scavenge reactive oxygen or nitrogen species or they may modulate the activity of signal transduction enzymes leading to changes in the expression of antioxidant genes. Alternatively, they may reduce plasma lipid levels by modulating lipid metabolic genes in tissues and thus reduce indirectly lipid-mediated oxidative and endoplasmic reticulum stress through their hypolipidemic effect. Here we review the proposed molecular mechanisms by which curcumin, a polyphenol present in the rhizomes of turmeric (Curcuma longa) spice, influences oxidative and lipid-mediated stress in the vascular system. At the molecular level, mounting experimental evidence suggests that curcumin may act chemically as scavenger of free radicals and/or influences signal transduction (e.g., Akt, AMPK) and modulates the activity of specific transcription factors (e.g., FOXO1/3a, NRF2, SREBP1/2, CREB, CREBH, PPARγ, and LXRα) that regulate the expression of genes involved in free radicals scavenging (e.g., catalase, MnSOD, and heme oxygenase-1) and lipid homeostasis (e.g., aP2/FABP4, CD36, HMG-CoA reductase, and carnitine palmitoyltransferase-I (CPT-1)). At the cellular level, curcumin may induce a mild oxidative and lipid-metabolic stress leading to an adaptive cellular stress response by hormetic stimulation of these cellular antioxidant defense systems and lipid metabolic enzymes. The resulting lower oxidative and lipid-mediated stress may not only explain the beneficial effects of curcumin on inflammation, cardiovascular, and neurodegenerative disease, but may also contribute to the increase in maximum life-span observed in animal models.

Demethoxycurcumin modulates prostate cancer cell proliferation via AMPK-induced down-regulation of HSP70 and EGFR

Curcumin (Cur), demethoxycurcumin (DMC), and bisdemethoxycurcumin (BDMC) are major forms of curcuminoids found in the rhizomes of turmeric. This study examined the effects of three curcuminoid analogues on prostate cancer cells. The results revealed that DMC demonstrated the most efficient cytotoxic effects on prostate cancer PC3 cells. DMC activated AMPK and in turn decreased the activity and/or expression of lipogenic enzymes, such as fatty acid synthase (FASN) and acetyl-CoA carboxylase (ACC). AICAR, an AMPK activator, and DMC down-regulated heat shock protein (HSP) 70 and increased the activity of the pro-apoptotic effector, caspase-3. In addition, DMC sustained epidermal growth factor receptor (EGFR) activation by suppressing the phosphatases PP2a and SHP-2. DMC also increased the interaction between EGFR and Cbl and induced the tyrosine phosphorylation of Cbl. The results suggest that DMC may have antitumor effects on prostate cancer cells via AMPK-induced down-regulation of HSP70 and EGFR.

Luteolin induces microRNA-132 expression and modulates neurite outgrowth in PC12 cells

Luteolin (3′,4′,5,7-tetrahydroxyflavone), a food-derived flavonoid, has been reported to exert neurotrophic properties that are associated with its capacity to promote neuronal survival and neurite outgrowth. In this study, we report for the first time that luteolin induces the persistent expression of microRNA-132 (miR-132) in PC12 cells. The correlation between miR-132 knockdown and a decrease in luteolin-mediated neurite outgrowth may indicate a mechanistic link by which miR-132 functions as a mediator for neuritogenesis. Furthermore, we find that luteolin led to the phosphorylation and activation of cAMP response element binding protein (CREB), which is associated with the up-regulation of miR-132 and neurite outgrowth. Moreover, luteolin-induced CREB activation, miR-132 expression and neurite outgrowth were inhibited by adenylate cyclase, protein kinase A (PKA) and MAPK/ERK kinase 1/2 (MEK1/2) inhibitors but not by protein kinase C (PKC) or calcium/calmodulin-dependent protein kinase II (CaMK II) inhibitors. Consistently, we find that luteolin treatment increases ERK phosphorylation and PKA activity in PC12 cells. These results show that luteolin induces the up-regulation of miR-132, which serves as an important regulator for neurotrophic actions, mainly acting through the activation of cAMP/PKA- and ERK-dependent CREB signaling pathways in PC12 cells.

The role of bioactive compounds on the promotion of neurite outgrowth

Neurite loss is one of the cardinal features of neuronal injury. Apart from neuroprotection, reorganization of the lost neuronal network in the injured brain is necessary for the restoration of normal physiological functions. Neuritogenic activity of endogenous molecules in the brain such as nerve growth factor is well documented and supported by scientific studies which show innumerable compounds having neurite outgrowth activity from natural sources. Since the damaged brain lacks the reconstructive capacity, more efforts in research are focused on the identification of compounds that promote the reformation of neuronal networks. An abundancy of natural resources along with the corresponding activity profiles have shown promising results in the field of neuroscience. Recently, importance has also been placed on understanding neurite formation by natural products in relation to neuronal injury. Arrays of natural herbal products having plentiful active constituents have been found to enhance neurite outgrowth. They act synergistically with neurotrophic factors to promote neuritogenesis in the diseased brain. Therefore use of natural products for neuroregeneration provides new insights in drug development for treating neuronal injury. In this study, various compounds from natural sources with potential neurite outgrowth activity are reviewed in experimental models.

Neurotrophic effect of citrus auraptene: neuritogenic activity in PC12 cells

The activation of extracellular signal-regulated kinases (ERK) leads to a number of cellular changes associated with the development of long-term memory. Using cultured cortical neurons, we previously showed that the n-hexane extract prepared from the peels of Citrus grandis (Kawachi bankan) induces the activation of ERK1/2 and that one of the compounds with this ability in the extract is 3,5,6,7,8,3′,4′-heptamethoxyflavone (HMF), a Citrus polymethoxyflavone. In fact, we found that HMF has the ability to rescue mice from drug-induced learning impairment. This hexane extract contains auraptene (AUR), a coumarin derivative with a monoterpene unit, together with HMF. The present study was designed to investigate the effect of AUR in vitro. Our results show that 1) AUR had the ability to induce the activation of ERK1/2 in not only cortical neurons but also the rat pheochromocytoma cell line (PC12 cells), which is a model system for studies on neuronal proliferation and differentiation; and 2) AUR had the ability to promote neurite outgrowth from PC12 cells.