Neurotrophic and neuroprotective effects of tripchlorolide, an extract of Chinese herb Tripterygium wilfordii Hook F, on dopaminergic neurons

Neurotrophic Natural Products

Neurotrophins (NGF, BDNF, NT3, NT4) can decrease cell death, induce differentiation, as well as sustain the structure and function of neurons, which make them promising therapeutic agents for the treatment of neurodegenerative disorders. However, neurotrophins have not been very effective in clinical trials mostly because they cannot pass through the blood-brain barrier owing to being high-molecular-weight proteins. Thus, neurotrophin-mimic small molecules, which stimulate the synthesis of endogenous neurotrophins or enhance neurotrophic actions, may serve as promising alternatives to neurotrophins. Small-molecular-weight natural products, which have been used in dietary functional foods or in traditional medicines over the course of human history, have a great potential for the development of new therapeutic agents against neurodegenerative diseases such as Alzheimer's disease. In this contribution, a variety of natural products possessing neurotrophic properties such as neurogenesis, neurite outgrowth promotion (neuritogenesis), and neuroprotection are described, and a focus is made on the chemistry and biology of several neurotrophic natural products.

The therapeutic potential of triptolide and celastrol in neurological diseases

Neurological diseases are complex diseases affecting the brain and spinal cord, with numerous etiologies and pathogenesis not yet fully elucidated. Tripterygium wilfordii Hook. F. (TWHF) is a traditional Chinese medicine with a long history of medicinal use in China and is widely used to treat autoimmune and inflammatory diseases such as systemic lupus erythematosus and rheumatoid arthritis. With the rapid development of modern technology, the two main bioactive components of TWHF, triptolide and celastrol, have been found to have anti-inflammatory, immunosuppressive and anti-tumor effects and can be used in the treatment of a variety of diseases, including neurological diseases. In this paper, we summarize the preclinical studies of triptolide and celastrol in neurological diseases such as neurodegenerative diseases, brain and spinal cord injury, and epilepsy. In addition, we review the mechanisms of action of triptolide and celastrol in neurological diseases, their toxicity, related derivatives, and nanotechnology-based carrier system.

A review: traditional herbs and remedies impacting pathogenesis of Parkinson's disease

Parkinson's disease (PD) is characterized by progressive degeneration of dopaminergic neurons, leading to misbalance and loss of coordination. Current therapies are claimed only for symptomatic relief, on long-term use, which causes alteration in basal ganglia, and give rise to various adverse effects like dyskinesia and extra pyramidal side effects, which is reversed and proved to be attenuated with the help of various herbal approaches. Therefore, in order to attenuate the dopaminergic complications, focus of current research has been shifted from dopaminergic to non-dopaminergic strategies. Herbs and herbal remedies seems to be a better option to overcome the complications associated with current dopaminergic therapies. In recent years, various herbs and herbal remedies based on Ayurveda, traditional Chinese and Korean remedies, have become the target of various researches. These herbs and their bioactive compound are being extensively used to treat PD in India, China, Japan, and Korea. The major focus of this current review is to analyze preclinical studies with reference to various herbs, bioactive compounds, and traditional remedies for the management of Parkinson disorder, which will give an insight towards clinical trials.

Treatment of Neurodegenerative Diseases with Bioactive Components of Tripterygium wilfordii

Tripterygium wilfordii Hook F. (TWHF), a traditional Chinese medicine, has been widely used to treat autoimmune and inflammatory diseases including rheumatoid arthritis, systemic lupus erythematosus and dermatomyositis in China. Recently, studies have demonstrated that the bioactive components of TWHF have effective therapeutic potential for neurodegenerative diseases including Alzheimer's disease, Parkinson's disease and Multiple Sclerosis. In this paper, we summarize the research progress of triptolide and celastrol (the two major TWHF components) as well as their analogues in the treatment of neurodegenerative diseases. In addition, we review and discuss the molecular mechanisms and structure features of those two bioactive TWHF components, highlighting their therapeutic promise in neurodegenerative diseases.

Tripchlorolide May Improve Spatial Cognition Dysfunction and Synaptic Plasticity after Chronic Cerebral Hypoperfusion

Chronic cerebral hypoperfusion (CCH) is a common pathophysiological mechanism that underlies cognitive decline and degenerative processes in dementia and other neurodegenerative diseases. Low cerebral blood flow (CBF) during CCH leads to disturbances in the homeostasis of hemodynamics and energy metabolism, which in turn results in oxidative stress, astroglia overactivation, and synaptic protein downregulation. These events contribute to synaptic plasticity and cognitive dysfunction after CCH. Tripchlorolide (TRC) is an herbal compound with potent neuroprotective effects. The potential of TRC to improve CCH-induced cognitive impairment has not yet been determined. In the current study, we employed behavioral techniques, electrophysiology, Western blotting, immunofluorescence, and Golgi staining to investigate the effect of TRC on spatial learning and memory impairment and on synaptic plasticity changes in rats after CCH. Our findings showed that TRC could rescue CCH-induced spatial learning and memory dysfunction and improve long-term potentiation (LTP) disorders. We also found that TRC could prevent CCH-induced reductions in N-methyl-D-aspartic acid receptor 2B, synapsin I, and postsynaptic density protein 95 levels. Moreover, TRC upregulated cAMP-response element binding protein, which is an important transcription factor for synaptic proteins. TRC also prevented the reduction in dendritic spine density that is caused by CCH. However, sham rats treated with TRC did not show any improvement in cognition. Because CCH causes disturbances in brain energy homeostasis, TRC therapy may resolve this instability by correcting a variety of cognitive-related signaling pathways. However, for the normal brain, TRC treatment led to neither disturbance nor improvement in neural plasticity. Additionally, this treatment neither impaired nor further improved cognition. In conclusion, we found that TRC can improve spatial learning and memory, enhance synaptic plasticity, upregulate the expression of some synaptic proteins, and increase the density of dendritic spines. Our findings suggest that TRC may be beneficial in the treatment of cognitive impairment induced by CCH.

Tissue engineered nigrostriatal pathway for treatment of Parkinson's disease

The classic motor deficits of Parkinson's disease are caused by degeneration of dopaminergic neurons in the substantia nigra pars compacta, resulting in the loss of their long-distance axonal projections that modulate the striatum. Current treatments only minimize the symptoms of this disconnection as there is no approach capable of replacing the nigrostriatal pathway. We are applying microtissue engineering techniques to create living, implantable constructs that mimic the architecture and function of the nigrostriatal pathway. These constructs consist of dopaminergic neurons with long axonal tracts encased within hydrogel microcolumns. Microcolumns were seeded with dopaminergic neuronal aggregates, while lumen extracellular matrix, growth factors, and end targets were varied to optimize cytoarchitecture. We found a 10-fold increase in axonal outgrowth from aggregates versus dissociated neurons, resulting in remarkable axonal lengths of over 6 mm by 14 days and 9 mm by 28 days in vitro. Axonal extension was also dependent upon lumen extracellular matrix, but did not depend on growth factor enrichment or neuronal end target presence. Evoked dopamine release was measured via fast scan cyclic voltammetry and synapse formation with striatal neurons was observed in vitro. Constructs were microinjected to span the nigrostriatal pathway in rats, revealing survival of implanted neurons while maintaining their axonal projections within the microcolumn. Lastly, these constructs were generated with dopaminergic neurons differentiated from human embryonic stem cells. This strategy may improve Parkinson's disease treatment by simultaneously replacing lost dopaminergic neurons in the substantia nigra and reconstructing their long-projecting axonal tracts to the striatum.

Neuroprotective Dihydroagarofuran Sesquiterpene Derivatives from the Leaves of Tripterygium wilfordii

Thirteen dihydroagarofuran derivatives, including 12 new sesquiterpenoid esters and one known sesquiterpenoid alkaloid, were obtained from the leaves of Tripterygium wilfordii. Spectroscopic techniques and the ECD method were used for the structure elucidation of the compounds. The structures of compounds 1 and 8 were confirmed by single-crystal X-ray crystallographic analyses. Compounds 8, 9, 11, 12, and 13 increased cell viability of the okadaic acid treated PC12 cells from 60.4 ± 23.0% to 72.4 ± 14.1, 71.5 ± 11.5, 75.7 ± 15.6, 81.2 ± 13.1, and 86.2 ± 25.5% at 10 μM, respectively.

Identification and functional characterization of diterpene synthases for triptolide biosynthesis from Tripterygium wilfordii

Tripterygium wilfordii, which has long been used as a medicinal plant, exhibits impressive and effective anti-inflammatory, immunosuppressive and anti-tumor activities. The main active ingredients are diterpenoids and triterpenoids, such as triptolide and celastrol, respectively. A major challenge to harnessing these natural products is that they are found in very low amounts in planta. Access has been further limited by the lack of knowledge regarding their underlying biosynthetic pathways, particularly for the abeo-abietane tri-epoxide lactone triptolide. Here suspension cell cultures of T. wilfordii were found to produce triptolide in an inducible fashion, with feeding studies indicating that miltiradiene is the relevant abietane olefin precursor. Subsequently, transcriptome data were used to identify eight putative (di)terpene synthases that were then characterized for their potential involvement in triptolide biosynthesis. This included not only biochemical studies which revealed the expected presence of class II diterpene cyclases that produce the intermediate copalyl diphosphate (CPP), along with the more surprising finding of an atypical class I (di)terpene synthase that acts on CPP to produce the abietane olefin miltiradiene, but also their subcellular localization and, critically, genetic analysis. In particular, RNA interference targeting either both of the CPP synthases, TwTPS7v2 and TwTPS9v2, or the subsequently acting miltiradiene synthase, TwTPS27v2, led to decreased production of triptolide. Importantly, these results then both confirm that miltiradiene is the relevant precursor and the relevance of the identified diterpene synthases, enabling future studies of the biosynthesis of this important bioactive natural product.

The Medicinal Chemistry of Natural and Semisynthetic Compounds against Parkinson's and Huntington's Diseases

Among the diseases affecting the central nervous system (CNS), neurodegenerations attract the interest of both the clinician and the medicinal chemist. The increasing average age of population, the growing number of patients, and the lack of long-term effective remedies push ahead the quest for novel tools against this class of pathologies. We present a review on the state of the art of the molecules (or combination of molecules) of natural origin that are currently under study against two well-defined pathologies: Parkinson's disease (PD) and Huntington's disease (HD). Nowadays, very few tools are available for preventing or counteracting the progression of such diseases. Two major parameters were considered for the preparation of this review: particular attention was reserved to these research works presenting well-defined molecular mechanisms for the studied compounds, and where available, papers reporting in vivo data were preferred. A literature search for peer-reviewed articles using PubMed, Scopus, and Reaxys databases was performed, exploiting different keywords and logical operators: 91 papers were considered (preferentially published after 2015). The review presents a brief overview on the etiology of the studied neurodegenerations and the current treatments, followed by a detailed discussion of the natural and semisynthetic compounds dividing them in different paragraphs considering their several mechanisms of action.

Neuroprotective mechanisms of plant extracts against MPTP induced neurotoxicity: Future applications in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease after Alzheimer's disease, affecting about seven to 10 million patients worldwide. The major pathological features of PD are loss of dopaminergic neurons in the nigrostriatal pathway and accumulation of alpha-synuclein molecules, forming Lewy bodies. Until now, there is no effective cure for PD, and investigators are searching for neuroprotective strategies to stop or slow the disease progression. The MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) induced neurotoxicity of the nigrostriatal pathway has been used to initiate PD in animal models. Multiple experimental studies showed the ability of several plant extracts to protect against MPTP induced neurotoxicity through activation of catalase, superoxide dismutase, and glutathione reductase enzymes, which reduce the cellular concentration of free radicals, preventing intracellular Ca⁺⁺ release and subsequent apoptosis signaling. Other neuroprotective mechanisms of plant extracts include promoting autophagy of alpha-synuclein molecules and exerting an antiapoptotic activity via inhibition of proteolytic poly (ADP-ribose) polymerase and preventing caspase cleavage. The variety of neuroprotective mechanisms of natural plant extracts may allow researchers to target PD progression in different pathological stages and may be through multiple pathways. Further investigations are required to translate these neuroprotective mechanisms into safe and effective treatments for PD.

Plant-Derived Natural Products for Parkinson's Disease Therapy

Plant-derived natural products have made their own niche in the treatment of neurological diseases since time immemorial. Parkinson's disease (PD), the second most prevalent neurodegenerative disorder, has no cure and the treatment available currently is symptomatic. This chapter thoughtfully and objectively assesses the scientific basis that supports the increasing use of these plant-derived natural products for the treatment of this chronic and progressive disorder. Proper considerations are made on the chemical nature, sources, preclinical tests and their validity, and mechanisms of behavioural or biochemical recovery observed following treatment with various plants derived natural products relevant to PD therapy. The scientific basis underlying the neuroprotective effect of 6 Ayurvedic herbs/formulations, 12 Chinese medicinal herbs/formulations, 33 other plants, and 5 plant-derived molecules have been judiciously examined emphasizing behavioral, cellular, or biochemical aspects of neuroprotection observed in the cellular or animal models of the disease. The molecular mechanisms triggered by these natural products to promote cell survivability and to reduce the risk of cellular degeneration have also been brought to light in this study. The study helped to reveal certain limitations in the scenario: lack of preclinical studies in all cases barring two; heavy dependence on in vitro test systems; singular animal or cellular model to establish any therapeutic potential of drugs. This strongly warrants further studies so as to reproduce and confirm these reported effects. However, the current literature offers scientific credence to traditionally used plant-derived natural products for the treatment of PD.

Triptolide treatment reduces Alzheimer's disease (AD)-like pathology through inhibition of BACE1 in a transgenic mouse model of AD

The complex pathogenesis of Alzheimer’s disease (AD) involves multiple contributing factors, including amyloid β (Aβ) peptide accumulation, inflammation and oxidative stress. Effective therapeutic strategies for AD are still urgently needed. Triptolide is the major active compound extracted from Tripterygium wilfordii Hook.f., a traditional Chinese medicinal herb that is commonly used to treat inflammatory diseases. The 5-month-old 5XFAD mice, which carry five familial AD mutations in the β-amyloid precursor protein (APP) and presenilin-1 (PS1) genes, were treated with triptolide for 8 weeks. We observed enhanced spatial learning performances, and attenuated Aβ production and deposition in the brain. Triptolide also inhibited the processing of amyloidogenic APP, as well as the expression of βAPP-cleaving enzyme-1 (BACE1) both in vivo and in vitro. In addition, triptolide exerted anti-inflammatory and anti-oxidative effects on the transgenic mouse brain. Triptolide therefore confers protection against the effects of AD in our mouse model and is emerging as a promising therapeutic candidate drug for AD.

Methyl 3,4-dihydroxybenzoate promotes neurite outgrowth of cortical neurons cultured in vitro

Cerebral cortical neurons from neonatal rats were cultured in the presence of methyl 3,4-dihydroxybenzoate (MDHB; 2, 4, and 8 μM). Results showed that MDHB significantly promoted neurite outgrowth and microtubule-associated protein 2 mRNA expression, and increased neuronal survival in a dose-dependent manner. Moreover, MDHB induced brain-derived neurotrophic factor expression. These findings suggest that MDHB has a neurotrophic effect, which may be due to its ability to increase brain-derived neurotrophic factor expression.

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.

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.

Tenuigenin protects dopaminergic neurons from inflammation-mediated damage induced by the lipopolysaccharide

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive death of dopaminergic neurons in the substantia nigra pars compacta (SNpc).

AIMS

To study if tenuigenin (TEN), the main active component of Polygala tenuifolia, can protect dopaminergic neurons from inflammation-mediated damage in vivo.

METHODS

We observed the effects of TEN on lipopolysaccharide (LPS) induced PD model by behavioral analysis, high-performance liquid chromatography, immunohistochemistry and enzyme-linked immunoadsorbent assay, etc.

RESULTS

We showed that a single intranigral dose of LPSs (10 μg) induced microglial activation, reduced the survival ratio of tyrosine hydroxylase-immunoreactive (TH-ir) neurons in the SNpc and reduced dopamine (DA) content in the striatum. Treatment with 300 mg/kg TEN once per day over 14 weeks improved the survival rate of TH-ir neurons in the SNpc to 75%, on the non-injected side. Treatment with 200 or 300 mg/kg TEN once per day over 14 weeks significantly improved DA levels in the striatum to 73% and 81% on the non-injected side, respectively. The excessive production of cytokines, such as tumor necrosis factor (TNF)-α and interleukin (IL)-1β, was abolished by TEN administration.

CONCLUSION

Our results suggest that TEN may play a role in protecting dopaminergic neurons against inflammatory challenge.

Triptolide with potential medicinal value for diseases of the central nervous system

Tripterygium wilfordii Hook.f. (TWHF) has a long history as a Traditional Chinese Medicine (TCM) herb that aids in treating inflammatory and autoimmune diseases. The major bioactive component of TWHF is triptolide, which has been recognized to possess a broad spectrum of biological profiles including antiinflammatory, immunosuppressive, antifertility, and antitumor activities, as well as neurotrophic and neuroprotective effects. Limitation of triptolide, such as poor water solubility and severe systemic toxicity, has postponed clinical development and trials; however, the wide range of medicinal value of triptolide has been drawing intensive worldwide attention. In particular, triptolide has been shown to have significant effects on central nervous system (CNS) diseases, such as Parkinson's disease, Alzheimer's disease, spinal cord and brain injury, and multiple sclerosis. This review focuses on the potential therapeutic role of triptolide on CNS diseases, and discusses the structural features, potential modifications, and the other pharmacological activities of triptolide.

LLDT-67 attenuates MPTP-induced neurotoxicity in mice by up-regulating NGF expression

AIM

To investigate the neuroprotective effects of LLDT-67, a novel derivative of triptolide, in MPTP-induced mouse Parkinson's disease (PD) models and in primary cultured astrocytes, and to elucidate the mechanisms of the action.

METHODS

In order to induce PD, C57BL/6 mice were injected MPTP (30 mg/kg, ip) daily from d 2 to d 6. MPTP-induced behavioral changes in the mice were examined using pole test, swimming test and open field test. The mice were administered LLDT-67 (1, 2, or 4 mg/kg, po) daily from d 1 to d 11. On d 12, the mice were decapitated and brains were collected for immunohistochemistry study and measuring monoamine levels in the striatum. Primary cultured astrocytes from the cortices of neonatal C57BL/6 mouse pups were prepared for in vitro study.

RESULTS

In MPTP-treated mice, administration of LLDT-67 significantly reduced the loss of tyrosine hydroxylase-positive neurons in the substantia nigra, and ameliorated the behavioral changes. LLDT-67 (4 mg/kg) significantly increased the expression of NGF in astrocytes in the substantia nigra and striatum of the mice. Furthermore, administration of LLDT-67 caused approximately 2-fold increases in the phosphorylation of TrkA at tyrosine 751, and marked increases in the phosphorylation of AKT at serine 473 as compared with the mice model group. In the cultured astrocytes, LLDT-67 (1 and 10 nmol/L) increased the NGF levels in the culture medium by 179% and 160%, respectively.

CONCLUSION

The neuroprotective effect of LLDT-67 can be mostly attributed to its ability to enhance NGF synthesis in astrocytes in the midbrain and to rescue dopaminergic neurons indirectly through TrkA activation.

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.

Extract of Tripterygium wilfordii Hook F Protect Dopaminergic Neurons Against Lipopolysaccharide-Induced Inflammatory Damage

Activation of microglia is a critical pathological marker of Parkinson's disease. Activated microglia produces proinflammatory and neurotoxic factors, which cause neurons to induce neurodegeneration. Although it is believed that Chinese herbs, such as Tripterygium wilfordii Hook F, can ease inflammatory diseases, little is known about its benefit to neurodegenerative disease, like Parkinson's disease. In this study, we report the extract of Tripterygium wilfordii Hook F with a novel extraction method significantly protected dopaminergic neurons from LPS-induced degeneration in rat mesencephalic neuron-glia cultures. Cells pretreated with the extract have shown dose-dependent inhibition of LPS-induced TNFα and excessive NO production. More importantly, the total number of activated microglia was greatly reduced in these pretreated cells. Our results suggest that the extract of Tripterygium wilfordii Hook F has a strong bioactive function to diminish the pro-inflammatory factors, such as TNFα and NO. These data might also shed light for future neurodegenerative disease therapy.

Anti-Parkinsonian drug discovery from herbal medicines: what have we got from neurotoxic models?

ETHNOPHARMACOLOGICAL RELEVANCE

Herbal medicines are used to treat Parkinson's disease (PD) in ancient medical systems in Asian countries such as India, China, Japan and Korea based on their own anecdotal or experience-based theories.

AIM OF THE REVIEW

To systematically summarize and analyze the anti-Parkinsonian activities of herbal preparations (including active compounds, herbal extracts and formulations) investigated in the neurotoxic models of PD and provide future references for basic and clinical investigations.

MATERIALS AND METHODS

All the herbal materials tested on in vitro and in vivo neurotoxic models of PD were retrieved from PubMed database by using pre-set searching strings. The relevant compounds and herbal extracts with anti-Parkinsonian activities were included and analyzed according to their chemical classifications or biological activities.

RESULTS

A total of 51 herbal medicines were analyzed. A diversity of compounds isolated from herbal materials were reported to be effective on neurotoxic models of PD by modulating multiple key events or signaling pathways implicated in the pathogenesis of PD. The main structure types of these compounds belong to catechols, stilbenoids, flavonoids, phenylpropanoids and lignans, phenylethanoid glycosides and terpenes. Although some herbal extracts and formulations have shown positive results on PD animal models, the relative compounds accounting for the effects and the underlying mechanisms remain to be further investigated.

CONCLUSIONS

Herbal medicines can be an alternative and valuable source for anti-Parkinsonian drug discovery. Compounds classified into stilbenoids, flavonoids, catechols and terpenes may be the most promising candidates for further investigation. Some well-studies compounds such as baicalein, puerarin, resveratrol, curcumin and ginsenosides deserve further consideration in clinical trials. In-depth experimental studies are still needed to evaluate the efficacy of herbal extracts and formulations in PD models.

Botanical Drugs and Stem Cells

The potential to generate virtually any differentiated cell type from stem cells offers the possibility of creating new sources of cells for regenerative medicine. To realize this potential, it will be essential to control stem cell differentiation. Chinese herbal medicine is a major aspect of traditional Chinese medicine and is a rich source of unique chemicals. As such, individual herbs or extracts may play a role in the proliferation and differentiation of stem cells. In this review, we discuss some of the Chinese herbal medicines that are used to treat human diseases such as neuronal degenerative diseases, cardiovascular diseases, and osteoporosis. We also describe the relationship between Chinese herbal medicines and stem cell regulation.

Neurotrophic activity of obovatol on the cultured embryonic rat neuronal cells by increase of neurotrophin release through activation of ERK pathway

Previously, we found that obovatol, a lignan compound isolated from Magnolia officinalis, has anti-cancer, anti-inflammatory, and anxiolytic effects. Recent studies showed that honokiol, magnolol, and 4-O-methylhonokiol, lignin compounds isolated from the Magnolia family have neurotrophic activity. In this study, we examined whether or not obovatol also exhibits neurite-promoting effects on rat embryonic neuronal cells. Obovatol increased neurite outgrowth in a concentration-dependent manner. Consistent with the neurite outgrowth effect, the expression of neurite differentiation markers also increased in response to obovatol. We also found that obovatol increased levels of NGF and BDNF released into the culture medium. In addition, the combination of low concentrations of obovatol (1 and 2 μM) with NGF (50 ng/ml) or with BDNF (10 ng/ml) greatly enhanced neurite outgrowth. Subsequently, we found that obovatol increased phosphorylation of ERK. However, the neurite outgrowth, and NGF and BDNF release induced by obovatol were prevented by an ERK-specific inhibitor. These results suggest that obovatol promotes neurite outgrowth due to the increased release of neurotrophic factors via activation of the ERK pathway.

Retrospect and prospect of active principles from Chinese herbs in the treatment of dementia

With an ageing population, dementia has become one of the world's primary health challenges. However, existing remedies offer limited benefits with certain side effects, which has prompted researchers to seek complementary and alternative therapies. China has long been known for abundant usage of various herbs. Some of these herbal decoctions are effective in stimulating blood circulation, supplementing vital energy and resisting aging, the lack of which are believed to underlie dementia. These herbs are regarded as new and promising sources of potential anti-dementia drugs. With the rapid evolution of life science and technology, numerous active components have been identified that are highly potent and multi-targeted with low toxicity, and therefore meet the requirements for dementia therapy. This review updates the research progress of Chinese herbs in the treatment of dementia, focusing on their effective principles.

Therapeutic strategies for Parkinson's disease: the ancient meets the future--traditional Chinese herbal medicine, electroacupuncture, gene therapy and stem cells

In China, it has been estimated that there are more than 2.0 million people suffering from Parkinson's disease, which is currently becoming one of the most common chronic neurodegenerative disorders during recent years. For many years, scientists have struggled to find new therapeutic approaches for this disease. Since 1994, our research group led by Drs. Ji-Sheng Han and Xiao-Min Wang of Neuroscience Research Institute, Peking University has developed several prospective treatment strategies for the disease. These studies cover the traditional Chinese medicine-herbal formula or acupuncture, and modern technologies such as gene therapy or stem cell replacement therapy, and have achieved some original results. It hopes that these data may be beneficial for the research development and for the future clinical utility for treatment of Parkinson's disease.

Tripchlorolide protects against MPTP-induced neurotoxicity in C57BL/6 mice

Many current studies of Parkinson's disease (PD) suggest that inflammation is involved in the neurodegenerative process. Tripchlorolide (TW397), a traditional Chinese herbal compound with anti-inflammatory and immunosuppressive properties, has been shown to protect dopaminergic neurons against, and restore their function after, the neurotoxicity induced by 1-methyl-4-phenylpyridinium ions in vitro. This study was designed to investigate the effect of TW397 in vivo in the PD model of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned C57BL/6 mice. In the animals that received vehicle-only (i.e., no TW397) treatment with MPTP i.p. injection, the survival ratios of tyrosine hydroxylase-immunoreactive (TH-IR) neurons in the substantia nigra pars compacta and TH-IR fibres in the striatum were only 59 and 13%, respectively, compared with the normal controls. Intriguingly, in conjunction with MPTP, treatment with TW397, 1 microg/kg for 16 days, once per day, dramatically improved the survival rate of the TH-IR neurons and TH-IR fibres to 80 and 43% of the control. The treatment with TW397 also significantly improved the level of dopamine in the substantia nigra and striatum to 157 and 191%, respectively, of the MPTP- plus vehicle-treated group. In addition, in MPTP-treated animals the rota-rod performances of those treated with 0.5 or 1 microg/kg TW397 were significantly improved, by approximately 2- and 3-fold, respectively, relative to vehicle-treated animals. The neuroprotective effect of TW397 was coincident with an attenuated astroglial response within the striatum. These data demonstrate a neuroprotective action of TW397 in vivo against MPTP toxicity, with important implications for the treatment of PD.

Triptolide upregulates NGF synthesis in rat astrocyte cultures

Triptolide (T10), an extract from the traditional Chinese herb, Tripterygium wilfordii Hook F (TWHF), has been shown to attenuate the rotational behavior induced by D: -amphetamine and prevent the loss of dopaminergic neurons in the substantia nigra in rat models of Parkinson's disease. To examine if the neuroprotective effect is mediated by its stimulation of production of neurotrophic factors from astrocytes, we investigated the effect of T10 on synthesis and release of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) in rat astrocyte cultures. T10 did not affect the synthesis and release of either BDNF or GDNF. However, it significantly increased NGF mRNA expression. It also increased both intracellular NGF and NGF level in culture medium. These results indicate that the neuroprotective effect of T10 might be mediated, at least in part, via a stimulation of the production and release of NGF in astrocytes.

3-Hydroxymorphinan, a metabolite of dextromethorphan, protects nigrostriatal pathway against MPTP-elicited damage both in vivo and in vitro

We investigated the neuroprotective property of analogs of dextromethorphan (DM) in lipopolysaccharide (LPS) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) models to identify neuroprotective drugs for Parkinson's disease (PD). In vivo studies showed that daily injections with DM analogs protected dopamine (DA) neurons in substantia nigra pars compacta and restored DA levels in striatum using two different models for PD. Of the five analogs studied, 3-hydroxymorphinan (3-HM), a metabolite of DM, was the most potent, and restored DA neuronal loss and DA depletion up to 90% of the controls. Behavioral studies showed an excellent correlation between potency for preventing toxin-induced decrease in motor activities and neuroprotective effects among the DM analogs studied, of which 3-HM was the most potent in attenuating behavioral damage. In vitro studies revealed two glia-dependent mechanisms for the neuroprotection by 3-HM. First, astroglia mediated the 3-HM-induced neurotrophic effect by increasing the gene expression of neurotrophic factors, which was associated with the increased acetylation of histone H3. Second, microglia participated in 3-HM-mediated neuroprotection by reducing MPTP-elicited reactive microgliosis as evidenced by the decreased production of reactive oxygen species. In summary, we show the potent neuroprotection by 3-HM in LPS and MPTP PD models investigated. With its high efficacy and low toxicity, 3-HM may be a novel therapy for PD.

Shedding light into the role of BDNF in the pharmacotherapy of Parkinson's disease

Parkinson's disease (PD) is a chronic, neurodegenerative disease with a 1% incidence in the population over 55 years of age. Movement impairments represent undoubtedly the hallmark of the disorder; however, extensive evidence implicates cognitive deficits as concomitant peculiar features. Brain-derived neurotrophic factor (BDNF) colocalizes with dopamine neurons in the substantia nigra, where dopaminergic cell bodies are located, and it has recently garnered attention as a molecule crucial for cognition, a function that is also compromised in PD patients. Thus, due to its colocalization with dopaminergic neurons and its role in cognition, BDNF might possess a dual role in PD, both as a neuroprotective molecule, since its inhibition leads to loss of nigral dopaminergic neurons, and as a neuromodulator, as its enhanced expression ameliorates cognitive processes. In this review, we discuss the mechanism of action of established as well as novel drugs for PD with a particular emphasis to those interfering with BDNF biosynthesis.

Triptolide protects dopaminergic neurons from inflammation-mediated damage induced by lipopolysaccharide intranigral injection

Converging lines of evidence suggest that neuroinflammatory processes may account for the progressive death of dopaminergic neurons in Parkinson's disease (PD). Therefore, anti-inflammatory strategies have attracted much interest for their potential to prevent further deterioration of PD. Our previous study showed that triptolide, a traditional Chinese herbal compound with anti-inflammatory and immunosuppressive properties, protected dopaminergic neurons from lipopolysaccharide (LPS)-induced damage in primary embryonic midbrain cell cultures. To examine further if triptolide can protect dopaminergic neurons from inflammation-mediated damage in vivo, microglial activation and injury of dopaminergic neurons were induced by LPS intranigral injection, and the effects of triptolide treatment on microglial activation and survival ratio and function of dopaminergic neurons were investigated. Our results demonstrated that microglial activation induced by a single intranigral dose of 10 mug of LPS reduced the survival ratio of tyrosine hydroxylase-immunoreactive (TH-ir) neurons in the substantia nigra pars compacta (SNpc) to 29% and the content of dopamine (DA) in striatum to 37% of the non-injected side. Intriguingly, treatment with triptolide of 5 mug/kg for 24 days once per day dramatically improved the survival rate of TH-ir neurons in the SNpc to 79% of the non-injected side. Meanwhile, treatment with triptolide of 1 or 5 mug/kg for 24 days once per day significantly improved DA level in striatum to 70% and 68% of the non-injected side, respectively. Complement receptor 3 (CR3) immunohistochemical staining revealed that triptolide treatment potently inhibited LPS-elicited deleterious activation of microglia in SNpc. The excessive production of cytokines, such as tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta, was significantly abolished by triptolide administration. These results, together with our previous data in vitro, highly suggest the effectiveness of triptolide in protecting dopaminergic neurons against inflammatory challenge.

Infusion of epidermal growth factor and basic fibroblast growth factor into the striatum of parkinsonian rats leads to in vitro proliferation and differentiation of adult neural progenitor cells

This study investigated the proliferation and differentiation of adult neural progenitor cells (aNPCs) derived from the striatum and substantia nigra (SN) of parkinsonian rats. We found that aNPCs isolated from the two areas of parkinsonian rats readily formed nestin-enriched neurospheres in vitro and exhibited an ability to differentiate into either neurons or astrocytes. Injection of epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) into the striatum of parkinsonian rats prior to the harvesting striatal aNPCs significantly increased the neurosphere formation rate and multiple differentiation capacity of these aNPCs when cultured in vitro. These data suggest that striatal and nigral adult NPCs in parkinsonian rats retain the abilities of proliferation and differentiation in vitro. In addition, exogenously applied growth factors could up-regulate the developmental potential of aNPCs. We conclude that our data supports the notion that endogenous cell replacement therapies may be useful for the future treatment of Parkinson's disease (PD).

Triptolide, a Chinese herbal extract, protects dopaminergic neurons from inflammation-mediated damage through inhibition of microglial activation

Mounting lines of evidence have suggested that brain inflammation participates in the pathogenesis of Parkinson's disease. Triptolide is one of the major active components of Chinese herb Tripterygium wilfordii Hook F, which possesses potent anti-inflammatory and immunosuppressive properties. We found that triptolide concentration-dependently attenuated the lipopolysaccharide (LPS)-induced decrease in [3H]dopamine uptake and loss of tyrosine hydroxylase-immunoreactive neurons in primary mesencephalic neuron/glia mixed culture. Triptolide also blocked LPS-induced activation of microglia and excessive production of TNFalpha and NO. Our data suggests that triptolide may protect dopaminergic neurons from LPS-induced injury and its efficiency in inhibiting microglia activation may underlie the mechanism.