Luteolin enhances cholinergic activities in PC12 cells through ERK1/2 and PI3K/Akt pathways

Luteolin Modulates Neural Stem Cells Fate Determination: In vitro Study on Human Neural Stem Cells, and in vivo Study on LPS-Induced Depression Mice Model

Luteolin is a natural flavone with neurotrophic effects observed on different neuronal cell lines. In the present study, we aimed to assess the effect of luteolin on hNSCs fate determination and the LPS-induced neuroinflammation in a mouse model of depression with astrocytogenesis defect. hNSCs were cultured in basal cell culture medium (control) or medium supplemented with luteolin or AICAR, a known inducer of astrogenesis. A whole-genome transcriptomic analysis showed that luteolin upregulated the expressions of genes related to neurotrophin, dopaminergic, hippo, and Wnt signaling pathways, and downregulated the genes involved in p53, TNF, FOXO, and Notch signaling pathways. We also found that astrocyte-specific gene GFAP, as well as other genes of the key signaling pathways involved in astrogenesis such as Wnt, BMP, and JAK-STAT pathways were upregulated in luteolin-treated hNSCs. On the other hand, neurogenesis and oligodendrogenesis-related genes, TUBB3, NEUROD 1 and 6, and MBP, were downregulated in luteolin-treated hNSCs. Furthermore, immunostaining showed that percentages of GFAP+ cells were significantly higher in luteolin- and AICAR-treated hNSCs compared to control hNSCs. Additionally, RT-qPCR results showed that luteolin upregulated the expressions of GFAP, BMP2, and STAT3, whereas the expression of TUBB3 remained unchanged. Next, we evaluated the effects of luteolin in LPS-induced mice model of depression that represents defects in astrocytogenesis. We found that oral administration of luteolin (10 mg/Kg) for eight consecutive days could decrease the immobility time on tail suspension test, a mouse behavioral test measuring depression-like behavior, and attenuate LPS-induced inflammatory responses by significantly decreasing IL-6 production in mice brain-derived astrocytes and serum, and TNFα and corticosterone levels in serum. Luteolin treatment also significantly increased mature BDNF, dopamine, and noradrenaline levels in the hypothalamus of LPS-induced depression mice. Though the behavioral effects of luteolin did not reach statistical significance, global gene expression analyses of mice hippocampus and brain-derived NSCs highlighted the modulatory effects of luteolin on different signaling pathways involved in the pathophysiology of depression. Altogether, our findings suggest an astrocytogenic potential of luteolin and its possible therapeutic benefits in neuroinflammatory and neurodegenerative diseases. However, further studies are required to identify the specific mechanism of action of luteolin.

Luteolin stimulates the NGF-induced neurite outgrowth in cultured PC12 cells through binding with NGF and potentiating its receptor signaling

Luteolin, a flavonoid in fruits and vegetables, has neurotrophic functions without a well-characterized mechanism. Here, we hypothesize a direct interaction of luteolin with nerve growth factor (NGF); as such, the functionality of the NGF could be potentiated. The direct binding of luteolin with NGF was validated by ultra-filtration, Biacore, and docking analyses. In cultured PC12 cells, application of luteolin in combination with a low dose of NGF potentiated the NGF-induced differentiation of neurons by an increase of the differentiated cell number to 25.4 ± 4.8% (p < 0.01), as well as the increased expression of neurofilaments by 119 ± 32.1% (p < 0.05), 191 ± 12.6% (p < 0.01), and 110 ± 23.4% (p < 0.05) for NF68, NF160 and NF200, respectively. The co-treatment induced the phosphorylations of tropomyosin receptor kinase A (TrkA), extracellular signal-regulated kinase 1/2 (ERK1/2), protein kinase B (Akt), phospholipase C-γ1 (PLCγ1), and cAMP response element-binding protein (CREB) by 2 to 3 fold: these induced phosphorylations were mimicking that of a high dose of NGF. Moreover, the application of the TrkA inhibitor, K252a, blocked the luteolin-mediated induction of neurofilament expression and neurite outgrowth in cultured PC12 cells, suggesting the target specificity. The result supports the development of luteolin as a therapeutic, or preventive, agent for NGF insufficiency-associated neurodegenerative diseases.

[Luteolin has a significant protective effect against cadmium-induced injury in lung epithelial Beas-2B cells]

OBJECTIVE

To investigate the protective effect of luteolin against cadmium (Cd)-induced injury in human lung epithelial Beas-2B cells.

OBJECTIVE

Beas-2B cells were treated with different concentrations of luteolin (0-160 μmol/L) or Cd (0-40 μmol/L) for 24 h, and the cell viability was examined using MTT assay. After treatment with luteolin (0.25, 0.5 and 0.75 μmol/L) with or without Cd (5 μmol/L) for 24 h, the cells were examined for viability, lactate dehydrogenase (LDH) activity and morphological changes of the cell nuclei using Hoechst fluorescent staining. The levels of ROS, SOD, GSH and MDA in the treated cells were detected, and the expression levels of Akt, p-Akt and nuclear factor E2-related factor 2 (Nrf2) proteins were determined using Western blotting.

OBJECTIVE

Luteolin within the concentration range of 0-80 μmol/L did not significantly affect the survival rate of Beas-2B cells (P>0.05), but Cd at 5 μmol/L significantly decreased the cell viability (P < 0.05) with an IC₅₀ of 24.6 μmol/L. In Cd-treated cells, treatment with luteolin significantly mitigated the decrease of cell viability, reduced LDH release and cell apoptosis, enhanced SOD activity and GSH content, and inhibited the production of MDA and ROS (all P < 0.05). Luteolin also significantly up-regulated the expression levels of p-Akt and Nrf2 protein in Cd-treated Beas-2B cells (P < 0.05).

OBJECTIVE

Luteolin has a significant protective effect against Cd-induced injury in Beas-2B cells, and the effects are probably mediated, at least in part, by promoting the activation of Akt and Nrf2.

Luteolin inhibits autophagy in allergic asthma by activating PI3K/Akt/mTOR signaling and inhibiting Beclin-1-PI3KC3 complex

Allergic asthma is a common chronic inflammatory disease characterized by airway inflammation, mucus hypersecretion and airway remodeling. Autophagy is a highly conserved intracellular degradation pathway in eukaryotic cells. There is growing evidence suggesting that dysregulation of autophagy is involved in the pathological process of asthma. Luteolin is a typical flavonoid compound with anti-inflammatory, anti-allergic and immune-enhancing functions. Previous studies have shown that luteolin can attenuate airway inflammation and hypersensitivity in asthma. However, whether luteolin can play a role in treating asthma by regulating autophagy remains unclear. The aim of the present study was to evaluate the therapeutic effect of luteolin on ovalbumin (OVA)-induced asthmatic mice, observe its effect on the level of autophagy in lung tissues, and further elucidate its underlying mechanism. The results showed that OVA-induced mice developed airway hyperresponsiveness, mucus over-production and collagen deposition. The number of inflammatory cells, levels of interleukin (IL)-4, IL-5 and IL-13 in bronchoalveolar lavage fluid (BALF) and OVA-specific IgE in serum were significantly increased. Furthermore, the infiltration of inflammatory cells was observed along with the activation of autophagy in lung tissues. Luteolin treatment significantly inhibited the OVA-induced inflammatory responses and the level of autophagy in lung tissues as well. Moreover, luteolin activated the PI3K/Akt/mTOR pathway and inhibited the Beclin-1-PI3KC3 protein complex in lung tissues of asthmatic mice. In conclusion, this study explored the regulatory mechanism of luteolin on autophagy in allergic asthma, providing biologic evidence for its clinical application.

Role of natural plant products against Alzheimer's disease

Alzheimer's disease (AD) is one of the major neurodegenerative disorder. Deposition of amyloid fibrils and tau protein are associated with various pathological symptoms. Currently limited medication is available for AD treatment. Most of the drugs are basically cholinesterase inhibitors and associated with various side effects. Natural plant products have shown potential as a therapeutic agent for the treatment of AD symptoms. Variety of secondary metabolites like flavonoids, tannins, terpenoids, alkaloids and phenols are used to reduce the progression of the disease. Plant products have less or no side effect and are easily available. The present review gives a detailed account of the potential of natural plant products against the AD symptoms.

Role of luteolin in overcoming Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder affecting elderly people (>60 years old) worldwide. There is no permanent cure for the disease but the symptomatic relief can be obtained by using dopamine agonists besides L-dopa therapy. The longer use of the drugs is associated with several side effects. Hence, the researchers have made a considerable attention toward the development of neuroprotective agents from plants. A number of phytochemicals have been demonstrated for their protective effects in various in vitro, in vivo, and clinical studies. In this context, luteolin, a flavone which is present in fruits and vegetables has been attributed to a number of pharmacological properties including neuroprotective. The present review demonstrates the bioavailability, oral absorption, and mechanism of action against PD.

In vitro cholinesterase inhibitory action of Cannabis sativa L. Cannabaceae and in silico study of its selected phytocompounds

Cannabis sativa L. Cannabaceae, used for psychoactive rituals in Mesopotamia. Here, we investigated in vitro inhibitory activity of methyl alcohol extract derived from leaves and resin of cannabis against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Moreover, the binding affinity (BA; kcal/mol) of selected phytochemicals of cannabis to AChE and BChE has been predicted in silico. Phytochemicals of cannabis had acceptable BA towards AChE ranging from  - 6.4 (beta-pinene) to  - 11.4 (campesterol) and BChE ranging from  - 5.5 (alpha-pinene) to  - 9.8 (cannabioxepane). All cannabinoids, flavonoids (apigenin), terpenes, and phytosterols of cannabis were double inhibitors due they utilized hydrogen bonds and hydrophobically interacted with both catalytic triad and peripheral anionic site (PAS) of AChE and BChE. Campesterol is phytosterol docked with AChE and BChE via hydrogen bond and it will be a lead-like molecule for further drug design. Delta-9-Tetrahydrocannabinolic acid has been docked with AChE and BChE and it can be a candidate molecule for further drug design. To sum up, this study not only approved cholinesterase inhibitory effects of cannabis but also suggested an array of phytocompounds as hit small molecules for discovery or design of ecofriendly botanical antiinsectants or phytonootropic drugs.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40203-021-00075-0.

Bioavailability and Pharmaco-therapeutic Potential of Luteolin in Overcoming Alzheimer's Disease

Luteolin is a naturally occurring, yellow crystalline flavonoid found in numerous dietary supplements we frequently have in our meals. Studies in the last 2 decades have revealed its therapeutic potential to reduce the Alzheimer's disease (AD) symptoms in various in vitro and in vivo models. The anti-Alzheimer's potential of luteolin is attributed to its ability to suppress Aβ as well as tau aggregation or promote their disaggregation, down-regulate the expression of COX-2, NOS, MMP-9, TNF-α, interleukins and chemokines, reduce oxidative stress by scavenging ROS, modulate the activities of transcription factors CREB, cJun, Nrf-1, NF-κB, p38, p53, AP-1 and β-catenine and inhibiting the activities of various protein kinases. In several systems, luteolin has been described as a potent antioxidant and anti-inflammatory agent. In addition, we have also discussed about the bio-availability of the luteolin in the plasma. After being metabolized luteolin persists in plasma as glucuronides and sulphate-conjugates. Human clinical trials indicated no dose limiting toxicity when administered at a dose of 100 mg/day. Improvements in the formulations and drug delivery systems may further enhance the bioavailability and potency of luteolin. The current review describes in detail the data supporting these studies.

A Pharmacological Appraisal of Neuroprotective and Neurorestorative Flavonoids Against Neurodegenerative Diseases

BACKGROUND & OBJECTIVE

Alzheimer's disease (AD) and Parkinson's disease (PD) affect an increasing number of the elderly population worldwide. The existing treatments mainly improve the core symptoms of AD and PD in a temporary manner and cause alarming side effects. Naturally occurring flavonoids are well-documented for neuroprotective and neurorestorative effects against various neurodegenerative diseases. Thus, we analyzed the pharmacokinetics of eight potent natural products flavonoids for the druggability and discussed the neuroprotective and neurorestorative effects and the underlying mechanisms.

CONCLUSION

This review provides valuable clues for the development of novel therapeutics against neurodegenerative diseases.

Chromium picolinate attenuates cognitive deficit in ICV-STZ rat paradigm of sporadic Alzheimer's-like dementia via targeting neuroinflammatory and IRS-1/PI3K/AKT/GSK-3β pathway

Alzheimer's disease (AD) is prevalent in old age people and is one of the most common brain diseases. Brain insulin resistance, neuroinflammation, oxidative stress, and mitochondrial and cholinergic dysfunction are key features of the disease. In our study, streptozotocin (STZ) in a dose of 3 mg/kg was injected in male Wistar rats bilaterally through the intracerebroventricular (ICV) route on stereotaxic apparatus. Chromium picolinate (CrPic) was tested at doses of 1 mg/kg, 2 mg/kg, and 4 mg/kg, while rivastigmine (2 mg/kg) was used as reference standard drug. Cognitive dysfunction induced by STZ was assessed by behavioral tests like Morris water maze and novel object recognition test. Treatment with CrPic revealed attenuation of cognitive deficit. This was confirmed by behavioral tests, biochemical estimations of antioxidant enzymes, oxidative stress, nitrosative stress, and cholinergic and mitochondrial activity. CrPic did not change AchE activity significantly. STZ-induced neuroinflammation evident by increased TNF-α, IL-6, and CRP levels was also significantly decreased by CrPic. Dysfunctional insulin signaling after ICV-STZ was demonstrated by reduced IRS-1, PI3K, AKT, BDNF gene expression, and increased GSK-3β, NF-κB gene expression with the help of qRT-PCR. CrPic treatment produced an improvement in insulin signaling revealed by increased gene expression of IRS-1, PI3-K, AKT, BDNF, and decreased gene expression of GSK-3β and NF-κB. It was concluded that CrPic reversed AD pathology revealed by improved memory, reduced oxidative stress, neuroinflammation, mitochondrial dysfunction, and upregulated insulin signaling.

Neuroprotective Polyphenols: A Modulatory Action on Neurotransmitter Pathways

BACKGROUND

Balance in neurotransmission is essential for the proper functioning of the nervous system and even a small, but prolonged disturbance, can induce the negative feedback mechanisms leading to various neuropathologies. Neurodegenerative and mood disorders such as Alzheimer's, Parkinson's or affective disorders are increasing medical and social problems. Among the wide spectrum of potentially destructive events, oxidative stress and disrupted metabolism of some neurotransmitters such as acetylcholine, GABA, glutamate, serotonin or dopamine appear to play a decisive role. Biologically active plant polyphenols have been shown to exert a positive impact on the function of the central nervous system by modulation of metabolism and the action of some neurotransmitters.

METHODS

Based on published research, the pharmacological activities of some naturally occurring polyphenols have been reviewed, with a focus on their potential therapeutic importance in the regulation of neurotransmitter systems.

RESULTS

Phytochemicals can be classified into several groups and most of them possess anticancer, antioxidative, anti-inflammatory and neuroprotective properties. They can also modulate the metabolism or action of some neurotransmitters and/or their receptors. Based on these properties, phytochemicals have been used in traditional medicine for ages, although it was focused mainly on treating symptoms. However, growing evidence indicates that polyphenols may also prevent or slow neurological diseases.

CONCLUSION

Phytochemicals seem to be less toxic than synthetic drugs and they can be a safer alternative for currently used preparations, which exert adverse side effects. The neuroprotective actions of some plant polyphenols in the regulation of neurotransmitters metabolism, functioning of neurotransmitters receptors and antioxidative defense have potential therapeutic applications in various neurodegenerative disorders.

Modulation of ERK1/2 and Akt Pathways Involved in the Neurotrophic Action of Caffeic Acid Alkyl Esters

Neurodegenerative diseases affect millions of human lives all over the world. The number of afflicted patients is rapidly growing, and disease-modifying agents are urgently needed. Caffeic acid, an important member of the hydroxycinnamic acid family of polyphenols, has considerable neurotrophic effects. We have previously shown how caffeate alkyl ester derivatives significantly promote survival and differentiation in neuronal cells. In this study, the mechanisms by which these ester derivatives exert their neurotrophic effects are examined. A series of eight caffeic acid esters with different alkyl chain lengths, ranging from methyl (CAF1) to dodecyl esters (CAF8), were synthesized and studied for their influence on neurotrophic signaling pathways. Caffeate esters did not induce tropomyosin-receptor kinase A (TrkA) phosphorylation, which was assessed by immunoblotting up to a concentration of 25 µM. NIH/3T3 cells overexpressing TrkA were generated to further examine phosphorylation of this receptor tyrosine kinase. None of the esters induced TrkA phosphorylation in these cells either. Assessment of the effect of caffeate derivatives on downstream neurotrophic pathways by immunoblotting showed that the most potent esters, decyl caffeate (CAF7) and dodecyl caffeate (CAF8) caused extracellular signal-regulated kinase (ERK1/2) and Akt serine threonine kinase phosphorylation in PC12 cells at 5 and 25 µM concentrations. In conclusion, this study shows that caffeate esters exert their neurotrophic action by modulation of ERK1/2 and Akt signaling pathways in neuronal cells, and further demonstrates the potential therapeutic implications of these derivatives for neurodegenerative diseases.

6-shogaol, a neuroactive compound of ginger (jahe gajah) induced neuritogenic activity via NGF responsive pathways in PC-12 cells

BACKGROUND

Ginger is a popular spice and food preservative. The rhizomes of the common ginger have been used as traditional medicine to treat various ailments. 6-Shogaol, a pungent compound isolated from the rhizomes of jahe gajah (Zingiber officinale var officinale) has shown numerous pharmacological activities, including neuroprotective and anti-neuroinflammatory activities. The aim of this study was to investigate the potential of 6-shogaol to mimic the neuritogenic activity of nerve growth factor (NGF) in rat pheochromocytoma (PC-12) cells.

METHODS

The cytotoxic effect of 6-shogaol was determined by 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The neuritogenic activity was assessed by neurite outgrowth stimulation assay while the concentration of extracellular NGF in cell culture supernatant was assessed by enzyme-linked immunosorbent assay (ELISA). Involvement of cellular signaling pathways, mitogen-activated protein kinase kinase/extracellular signal-regulated kinase1/2 (MEK/ERK1/2) and phosphoinositide-3-kinase/protein kinase B (PI3K/AKT) in 6-shogaol-stimulated neuritogenesis were examined by using specific pharmacological inhibitors.

RESULTS

6-Shogaol (500 ng/ml) induced neuritogenesis that was comparable to NGF (50 ng/ml) and was not cytotoxic towards PC-12 cells. 6-Shogaol induced low level of NGF biosynthesis in PC-12 cells, showing that 6-shogaol stimulated neuritogenesis possibly by inducing NGF biosynthesis, and also acting as a substitute for NGF (NGF mimic) in PC-12 cells. The inhibitors of Trk receptor (K252a), MEK/ERK1/2 (U0126 and PD98059) and PI3K/AKT (LY294002) attenuated the neuritogenic activity of both NGF and 6-shogaol, respectively.

CONCLUSIONS

The present findings demonstrated that 6-shogaol induced neuritogenic activity in PC-12 cells via the activation MEK/ERK1/2 and PI3K/AKT signaling pathways. This study suggests that 6-shogaol could act as an NGF mimic, which may be beneficial for preventive and therapeutic uses in neurodegenerative diseases.

N-Propargyl Caffeamide (PACA) Ameliorates Dopaminergic Neuronal Loss and Motor Dysfunctions in MPTP Mouse Model of Parkinson's Disease and in MPP+-Induced Neurons via Promoting the Conversion of proNGF to NGF

Insufficient production of nerve growth factor (NGF) is implicated in Parkinson's disease (PD). We recently discovered that caffeic acid derivative N-propargyl caffeamide (PACA) not only potentiated NGF-induced neurite outgrowth but also attenuated 6-hydroxydopamine neurotoxicity in neuronal culture. The aim of the present study was to investigate whether PACA could increase NGF levels against 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) neurotoxicity in a mouse PD model. We induced parkinsonism in mice by intraperitoneal injection of MPTP for seven consecutive days. Animal motor functions were assessed by rotarod test and pole test. Our results showed that PACA ameliorated motor impairments in MPTP-challenged mice. Based on Western blot analysis and/or immunofluorescence staining of NGF and tyrosine hydroxylase (TH), PACA preserved TH levels in the midbrain substantia nigra pars compacta. PACA also increased NGF expression while it decreased proNGF accumulation. Interestingly, NGF was widely induced in the midbrains including astrocytes. To elucidate the mechanisms by which PACA induces NGF, we focused on the effects of PACA on two neurotrophic signaling pathways, the PI3K and MEK pathways. We found that PACA induced the phosphorylation of Akt, ERK, and CREB against MPTP-mediated alterations. Importantly, PACA increased NGF levels and subsequently induced TrkA activation in MPTP-treated mice. Consistently, PACA also increased NGF levels in dopaminergic PC12 cells and primary rat midbrain neurons against N-methyl-4-phenylpyridinium iodide (MPP⁺) toxicity. ERK and PI3K inhibitors attenuated the effects of PACA on NGF levels. Collectively, our results suggest that PACA may rescue NGF insufficiency via sequential activation of PI3K/Akt, ERK1/2, and CREB signaling pathways. Graphical Abstract ᅟ.

Lactucopicrin potentiates neuritogenesis and neurotrophic effects by regulating Ca2+/CaMKII/ATF1 signaling pathway

ETHNO-PHARMACOLOGICAL RELEVANCE

Lactucopicrin is one of constitutes in Cichorium intybus L, which is commonly known as chicory in worldwide. It has been used for traditional usage such as antianalgesics, antidepressants and antihyperglycemics AIM OF STUDY: We investigated the neurotrophin-mediated neuroprotective effect of lactucopicrin in in vitro and examined for the underlying mechanism.

MATERIALS AND METHOD

To verify the neuroprotective effect of lactucopicrin, we investigated the inhibitory AChE activity, neurite outgrowth-related downstream signaling in murine neuroblastoma N2a and neurotrophins secretion in rat C6 glioma cells.

RESULTS

Lactucopicrin inhibited the AChE activity and increased intracellular Ca²⁺ levels with a substantial rise in muscarinic acetylcholine receptor M1 (CHRM1) expression in N2a cells. Moreover, lactucopicrin actively promoted neurite outgrowth via Ca²⁺-mediated activation of Ca²⁺/calmodulin-dependent protein kinase-II (CaMKII). It further activates transcription factor 1 (ATF1) along with modulating the levels of tropomyosin receptor kinase A, extracellular signal-regulated kinase 1 and 2, AKT, and synaptophysin 1 in N2a cells. Additionally, the levels of neurotrophins including NGF, BDNF, and NT3 were increased by treatment of lactucopicrin in C6 cells. The effects of lactucopicrin on NGF secretion and neuritogenesis were maintained even in the presence of phosphatidylinositol-3-kinase (PI3K) inhibitor LY294002, indicating that lactucopicrin exerts its effect on neuritogenesis in a PI3K-independent manner.

CONCLUSION

Our results suggest that the natural compound lactucopicrin may be a promising neurotrophin-mediated neuroprotective candidate for neurodegenerative diseases.

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.

Anti-neuropathic effects of Rosmarinus officinalis L. terpenoid fraction: relevance of nicotinic receptors

Traditional uses and current results highlight the neuroprotective properties of Rosmarinus officinalis L. The compelling need for novel strategies able to relieve neuropathic pain encouraged us to analyze different rosemary leaf extracts in rats following chronic constriction injury (CCI) of sciatic nerve. Ethanol, acetone, and the innovative ultrasound-hexane extractive methods were used to obtain: EE, AE, and for hexane extracts UREprel and URE. Extracts were characterized in terms of typical constituents and repeatedly administered to CCI-rats (13-days treatment, from the day of surgery). URE showed the best efficacy and potency in reducing hypersensitivity to noxious- and non-noxious stimuli and spontaneous pain. URE contained the higher quantity of the terpenoid carnosic acid (CA) and its efficacy was compared to pure CA. Histological analysis of the sciatic nerve revealed that URE prevented axon and myelin derangement, edema and inflammatory infiltrate. In the dorsal horn of the spinal cord, URE did not reduce astrocyte activation. Both the pain reliever and the neuroconservative effects of URE were significantly prevented by the nicotinic receptor (nAChR) antagonist mecamylamine. In conclusion, the hexane-ultrasound rosemary extract is able to reduce neuropathic hypersensitivity and protect nervous tissues. Effectiveness is mainly related to the terpenoid fraction by mechanisms involving nAChRs.

Chronic over-nutrition and dysregulation of GSK3 in diseases

Loss of cellular response to hormonal regulation in maintaining metabolic homeostasis is common in the process of aging. Chronic over-nutrition may render cells insensitive to such a hormonal regulation owing to overstimulation of certain signaling pathways, thus accelerating aging and causing diseases. The glycogen synthase kinase 3 (GSK3) plays a pivotal role in relaying various extracellular and intracellular regulatory signals critical to cell growth, survival, regeneration, or death. The main signaling pathway regulating GSK3 activity through serine-phosphorylation is the phosphoinositide 3-kinase (PI3K)/phosphoinositide-dependent kinase-1 (PDK1)/Akt relay that catalyzes serine-phosphorylation and thus inactivation of GSK3. In addition, perilipin 2 (PLIN2) has recently been shown to regulate GSK3 activation through direct association with GSK3. This review summarizes current understanding on environmental and nutritional factors contributing to GSK3 regulation (or dysregulation) through the PI3K/PDK1/Akt/GSK3 axis, and highlights the newly discovered role that PLIN2 plays in regulating GSK3 activity and GSK3 downstream pathways.

New perspectives for multi-level regulations of neuronal acetylcholinesterase by dioxins

Acetylcholinesterase (AChE; EC 3.1.1.7) is a vital functional enzyme in cholinergic neurotransmission which can rapidly hydrolyze neurotransmitter, acetylcholine, in the central and peripheral nervous systems. Emerging evidence showed that in addition to classical environmental AChE inhibitors, e.g. organophosphate and carbamate pesticides, dioxins are a new type of xenobiotic causing impairment of AChE. Dioxin can transcriptionally or post-transcriptionally suppress AChE expression in human neuroblastoma cells or mouse immune cells via the aryl hydrocarbon receptor (AhR) pathway, respectively. Dioxins can affect gene expression through other mechanisms, such as cross-talk with other signaling cascades and epigenetic modulations. Therefore, in this review, by summarizing the known mechanisms of AChE regulation and dioxin-induced gene alteration, potential signaling cascades and epigenetic mechanisms are proposed for dioxin-mediated AChE regulation. Mitogen activated protein (MAP) kinase, 3', 5'-cyclic adenosine monophosphate (cAMP) and calcium-related singaling pathways, as well as potential epigenetic mechanisms, such as DNA methylation, and post-transcriptional regulation via microRNAs, including hsa-miR-132, hsa-miR-212 and hsa-miR-25-3p are discussed here. These proposed mechanisms may be invaluable not only to promote comprehensive understanding of the action mechanisms for dioxin, but to illustrate the molecular basis of dioxin-induced health impacts.

Minocycline Promotes Neurite Outgrowth of PC12 Cells Exposed to Oxygen-Glucose Deprivation and Reoxygenation Through Regulation of MLCP/MLC Signaling Pathways

Minocycline, a semi-synthetic second-generation derivative of tetracycline, has been reported to exert neuroprotective effects both in animal models and in clinic trials of neurological diseases. In the present study, we first investigated the protective effects of minocycline on oxygen-glucose deprivation and reoxygenation-induced impairment of neurite outgrowth and its potential mechanism in the neuronal cell line, PC12 cells. We found that minocycline significantly increased cell viability, promoted neurite outgrowth and enhanced the expression of growth-associated protein-43 (GAP-43) in PC12 cells exposed to oxygen-glucose deprivation/reoxygenation injury. In addition, immunoblots revealed that minocycline reversed the overexpression of phosphorylated myosin light chain (MLC) and the suppression of activated extracellular signal-regulated kinase 1/2 (ERK1/2) caused by oxygen-glucose deprivation/reoxygenation injury. Moreover, the minocycline-induced neurite outgrowth was significantly blocked by Calyculin A (1 nM), an inhibitor of myosin light chain phosphatase (MLCP), but not by an ERK1/2 inhibitor (U0126; 10 μM). These findings suggested that minocycline activated the MLCP/MLC signaling pathway in PC12 cells after oxygen-glucose deprivation/reoxygenation injury, which resulted in the promotion of neurite outgrowth.

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.

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

AIM

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.

METHODS

We investigated the neuroprotective and neurotrophic activities of puerarin in MPTP-lesioned mice and dopaminergic PC12 cells. The effects of puerarin on ERK1/2, Akt, Nrf2, and HO-1 were assessed by Western blotting. The neurite outgrowth was assayed by neurite outgrowth staining kit.

RESULTS

Puerarin protected dopaminergic cells and ameliorated the behavioral impairments in MPTP-lesioned mice. Puerarin potentiated the effect of NGF on neuritogenesis in PC12 cells by >10-fold. Mechanistic studies revealed: (1) puerarin rapidly activated ERK1/2 and Akt, leading to the activation of Nrf2/heme oxygenase-1 (HO-1) pathways; (2) ERK1/2, PI3K/Akt, and HO-1 inhibitors attenuated the neuritogenic activity of puerarin. Notably, puerarin enhanced NGF-induced neuritogenesis in a timing-dependent manner.

CONCLUSION

Puerarin effectively coordinated with NGF to stimulate neuritogenesis via activating ERK1/2 and PI3K/Akt pathways in neurite extension process. These results demonstrated a general mechanism supporting the therapeutic application of puerarin-related compounds in neurodegenerative diseases.

Nutraceuticals in cognitive impairment and Alzheimer's disease

Several chemical substances belonging to classes of natural dietary origin display protective properties against some age-related diseases including neurodegenerative ones, particularly Alzheimer's disease (AD). These compounds, known as nutraceuticals, differ structurally, act therefore at different biochemical and metabolic levels and have shown different types of neuroprotective properties. The aim of this review is to summarize data from observational studies, clinical trials, and randomized clinical trials (RCTs) in humans on the effects of selected nutraceuticals against age-related cognitive impairment and dementia. We report results from studies on flavonoids, some vitamins and other natural substances that have been studied in AD and that might be beneficial for the maintenance of a good cognitive performance. Due to the substantial lack of high-level evidence studies there is no possibility for recommendation of nutraceuticals in dementia-related therapeutic guidelines. Nevertheless, the strong potential for their neuroprotective action warrants further studies in the field.

Neurotrophic natural products: chemistry and biology

Neurodegenerative diseases and spinal cord injury affect approximately 50 million people worldwide, bringing the total healthcare cost to over 600 billion dollars per year. Nervous system growth factors, that is, neurotrophins, are a potential solution to these disorders, since they could promote nerve regeneration. An average of 500 publications per year attests to the significance of neurotrophins in biomedical sciences and underlines their potential for therapeutic applications. Nonetheless, the poor pharmacokinetic profile of neurotrophins severely restricts their clinical use. On the other hand, small molecules that modulate neurotrophic activity offer a promising therapeutic approach against neurological disorders. Nature has provided an impressive array of natural products that have potent neurotrophic activities. This Review highlights the current synthetic strategies toward these compounds and summarizes their ability to induce neuronal growth and rehabilitation. It is anticipated that neurotrophic natural products could be used not only as starting points in drug design but also as tools to study the next frontier in biomedical sciences: the brain activity map project.

Hericium erinaceus (Bull.: Fr) Pers. cultivated under tropical conditions: isolation of hericenones and demonstration of NGF-mediated neurite outgrowth in PC12 cells via MEK/ERK and PI3K-Akt signaling pathways

Hericium erinaceus is an edible and medicinal mushroom used traditionally to improve memory.

Nature as a source of metabolites with cholinesterase-inhibitory activity: an approach to Alzheimer's disease treatment

Objectives

Alzheimer's disease (AD) is the most common cause of dementia, being responsible for high healthcare costs and familial hardships. Despite the efforts of researchers, no treatment able to delay or stop AD progress exists. Currently, the available treatments are only symptomatic, cholinesterase inhibitors being the most widely used drugs. Here we describe several natural compounds with anticholinesterase (acetylcholinesterase and butyrylcholinesterase) activity and also some synthetic compounds whose structures are based on those of natural compounds.

Key findings

Galantamine and rivastigmine are two cholinesterase inhibitors used in therapeutics: galantamine is a natural alkaloid that was extracted for the first time from Galanthus nivalis L., while rivastigmine is a synthetic alkaloid, the structure of which is modelled on that of natural physostigmine. Alkaloids include a high number of compounds with anticholinesterases activity at the submicromolar range. Quinones and stilbenes are less well studied regarding cholinesterase inhibition, although some of them, such as sargaquinoic acid or (+)-α-viniferin, show promising activity. Among flavonoids, flavones and isoflavones are the most potent compounds. Xanthones and monoterpenes are generally weak cholinesterase inhibitors.

Summary

Nature is an almost endless source of bioactive compounds. Several natural compounds have anticholinesterase activity and others can be used as leader compounds for the synthesis of new drugs.

Rosmarinus officinalis polyphenols produce anti-depressant like effect through monoaminergic and cholinergic functions modulation

Rosmarinus officinalis (R. officinalis), a culinary aromatic and medicinal plant, is very rich in polyphenols and flavonoids with high antioxidant properties. This plant was reported to exert multiple benefits for neuronal system and alleviate mood disorder. In our previous study, we demonstrated that R. officinalis and its active compounds, luteolin (Lut), carnosic acid (CA), and rosmarinic acid (RA), exhibited neurotrophic effects and improved cholinergic functions in PC12 cells in correlation with mitogen-activated protein kinase (MAPK), ERK1/2 signaling pathway. The current study was conducted to evaluate and understand the anti-depressant effect of R. officinalis using tail suspension test (TST) in ICR mice and PC12 cells as in vitro neuronal model. Proteomics analysis of PC12 cells treated with R. officinalis polyphenols (ROP) Lut, CA, and RA revealed a significant upregulation of tyrosine hydroxylase (TH) and pyruvate carboxylase (PC) two major genes involved in dopaminergic, serotonergic and GABAergic pathway regulations. Moreover, ROP were demonstrated to protect neuronal cells against corticosterone-induced toxicity. These results were concordant with decreasing immobility time in TST and regulation of several neurotransmitters (dopamine, norepinephrine, serotonin and acetylcholine) and gene expression in mice brain like TH, PC and MAPK phosphatase (MKP-1). To the best of our knowledge this is the first evidence to contribute to the understanding of molecular mechanism behind the anti-depressant effect of R. officinalis and its major active compounds.