Celastrol, a potent antioxidant and anti-inflammatory drug, as a possible treatment for Alzheimer's disease

Celastrol, a triterpene extracted from the Chinese "Thunder of God Vine," is a potent proteasome inhibitor and suppresses human prostate cancer growth in nude mice

Interest in the use of traditional medicines for cancer prevention and treatment is increasing. In vitro, in vivo, and clinical studies suggest the potential use of proteasome inhibitors as novel anticancer drugs. Celastrol, an active compound extracted from the root bark of the Chinese medicine "Thunder of God Vine" (Tripterygium wilfordii Hook F.), was used for years as a natural remedy for inflammatory conditions. Although Celastrol has been shown to induce leukemia cell apoptosis, the molecular target involved has not been identified. Furthermore, whether Celastrol has antitumor activity in vivo has never been conclusively shown. Here, we report, for the first time, that Celastrol potently and preferentially inhibits the chymotrypsin-like activity of a purified 20S proteasome (IC(50) = 2.5 micromol/L) and human prostate cancer cellular 26S proteasome (at 1-5 micromol/L). Inhibition of the proteasome activity by Celastrol in PC-3 (androgen receptor- or AR-negative) or LNCaP (AR-positive) cells results in the accumulation of ubiquitinated proteins and three natural proteasome substrates (IkappaB-alpha, Bax, and p27), accompanied by suppression of AR protein expression (in LNCaP cells) and induction of apoptosis. Treatment of PC-3 tumor-bearing nude mice with Celastrol (1-3 mg/kg/d, i.p., 1-31 days) resulted in significant inhibition (65-93%) of the tumor growth. Multiple assays using the animal tumor tissue samples from both early and end time points showed in vivo inhibition of the proteasomal activity and induction of apoptosis after Celastrol treatment. Our results show that Celastrol is a natural proteasome inhibitor that has a great potential for cancer prevention and treatment.

Chronic inhibition of cardiac Kir2.1 and HERG potassium channels by celastrol with dual effects on both ion conductivity and protein trafficking

A high percentage of drugs and drug candidates has been found to cause cardiotoxicity by reducing potassium conductance, more commonly known as QT prolongation. However, some compounds do not show direct block of ionic flow, suggesting that other mechanisms may also lead to reduction of potassium currents. Using the functional recovery after chemobleaching (FRAC) assay, we have examined a collection of drugs and drug-like compounds for potential perturbation of cardiac potassium channel trafficking. Here we report that a significant number of inhibitory compounds displayed effects on channel expression on the cell surface. Further investigation of celastrol (3-hydroxy-24-nor-2-oxo-1 (10),3,5,7-friedelatetraen-29-oic acid), a cell-permeable dienonephenolic triterpene compound, revealed its potent inhibitory activity on both Kir2.1 and hERG potassium channels, causal to QT prolongation. In addition to acute block of ion conduction, celastrol also alters the rate of ion channel transport and causes a reduction of channel density on the cell surface. In contrast, celastrol has no effects on trafficking of either CD4 or CD8 membrane proteins. Furthermore, the potency for reducing surface expression is approximately 5-10-fold more effective than that for either direct acute inhibition or reported cytoprotectivity via activation of the heat shock transcription factor 1. Because the reduction of potassium channel activity is a common form of druginduced cardiotoxicity, the potent inhibition of cell surface expression by celastrol underscores a need to evaluate drug candidates for their chronic effects on biogenesis of potassium channels. Our results suggest that chronic exposure to certain drugs may be an important aspect of acquired QT prolongation.

Determination of triptolide in root extracts of Tripterygium wilfordii by solid-phase extraction and reverse-phase high-performance liquid chromatography

Extracts of Tripterygium wilfordii roots have a long history of use in traditional Chinese medicine and have shown great promise in recent clinical trials as a treatment for rheumatoid arthritis. The major active component of Tripterygium root extracts is the diterpenoid triptolide. This paper describes a method for the determination of triptolide in root extracts that is suitable for the analysis of many small samples simultaneously. Extracts are applied to aminopropyl solid-phase extraction (SPE) tubes that are then eluted with dichloromethane-methanol (49:1, v/v). The eluate is chromatographed on a pentafluorophenyl HPLC column using an acetonitrile:water gradient. Triptolide is quantified by ultraviolet detection at 219 nm. Using this method, it was shown that smaller diameter roots with secondary growth contained higher triptolide concentrations than larger roots. This suggests that roots to be used for production of the drug extract could be harvested while still small, which would reduce the growing time necessary and thus be economically beneficial for the growers.

Celastrol protects against MPTP- and 3-nitropropionic acid-induced neurotoxicity

Oxidative stress and inflammation are implicated in neurodegenerative diseases including Parkinson's disease (PD) and Huntington's disease (HD). Celastrol is a potent anti-inflammatory and antioxidant compound extracted from a perennial creeping plant belonging to the Celastraceae family. Celastrol is known to prevent the production of proinflammatory cytokines, inducible nitric oxide synthase and lipid peroxidation. Mice were treated with celastrol before and after injections of MPTP, a dopaminergic neurotoxin, which produces a model of PD. A 48% loss of dopaminergic neurons induced by MPTP in the substantia nigra pars compacta was significantly attenuated by celastrol treatment. Moreover, celastrol treatment significantly reduced the depletion in dopamine concentration induced by MPTP. Similarly, celastrol significantly decreased the striatal lesion volume induced by 3-nitropropionic acid, a neurotoxin used to model HD in rats. Celastrol induced heat shock protein 70 within dopaminergic neurons and decreased tumor necrosis factor-alpha and nuclear factor kappa B immunostainings as well as astrogliosis. Celastrol is therefore a promising neuroprotective agent for the treatment of PD and HD.

Peroxynitrite production and NOS expression in astrocytes U373MG incubated with lipoproteins from Alzheimer patients

Apolipoprotein E (apo E), a plasma protein involved both in the metabolism of cholesterol and triglycerides, particularly in nervous tissue, has been associated with a higher risk of Alzheimer's disease. It has been shown that apo E increased the production of nitric oxide (NO) from human monocyte-derived macrophages (MDM); this effect could represent an important link between tissue redox balance and inflammation, since inflammation and oxidative stress are involved in chronic neurodegenerative disorders. Moreover, it has been evidenced that an overproduction of NO in the central nervous system (CNS) may play a key role in aging and that the glial cells (microglials cells and probably astrocytes) are able to form consistent amounts of NO through the induction of a nitric oxide synthase (iNOS) isoform so-called inducible or inflammatory. This report was performed in order to elucidate the effects produced by lipoproteins from control subjects, AD patients and first degree relatives (offspring) on human astrocyte cells after a short incubation. Peroxynitrite and NO production and NOS expression in cultured astrocytes were measured. We observed a decreased NO production after incubation with both LDL and HDL and an increased peroxynitrite production. As it concerns NOS expression, densitometric analysis of bands indicated that iNOS protein levels were significantly higher in the cells incubated with both AD lipoproteins and offspring lipoproteins compared to cells incubated with control lipoproteins. These findings suggest the possibility to identify in NO pathway a precocious marker of AD.

Reversal of a full-length mutant huntingtin neuronal cell phenotype by chemical inhibitors of polyglutamine-mediated aggregation

BACKGROUND

Huntington's disease (HD) is an inherited neurodegenerative disorder triggered by an expanded polyglutamine tract in huntingtin that is thought to confer a new conformational property on this large protein. The propensity of small amino-terminal fragments with mutant, but not wild-type, glutamine tracts to self-aggregate is consistent with an altered conformation but such fragments occur relatively late in the disease process in human patients and mouse models expressing full-length mutant protein. This suggests that the altered conformational property may act within the full-length mutant huntingtin to initially trigger pathogenesis. Indeed, genotype-phenotype studies in HD have defined genetic criteria for the disease initiating mechanism, and these are all fulfilled by phenotypes associated with expression of full-length mutant huntingtin, but not amino-terminal fragment, in mouse models. As the in vitro aggregation of amino-terminal mutant huntingtin fragment offers a ready assay to identify small compounds that interfere with the conformation of the polyglutamine tract, we have identified a number of aggregation inhibitors, and tested whether these are also capable of reversing a phenotype caused by endogenous expression of mutant huntingtin in a striatal cell line from the HdhQ111/Q111 knock-in mouse.

RESULTS

We screened the NINDS Custom Collection of 1,040 FDA approved drugs and bioactive compounds for their ability to prevent in vitro aggregation of Q58-htn 1-171 amino terminal fragment. Ten compounds were identified that inhibited aggregation with IC50 < 15 microM, including gossypol, gambogic acid, juglone, celastrol, sanguinarine and anthralin. Of these, both juglone and celastrol were effective in reversing the abnormal cellular localization of full-length mutant huntingtin observed in mutant HdhQ111/Q111 striatal cells.

CONCLUSIONS

At least some compounds identified as aggregation inhibitors also prevent a neuronal cellular phenotype caused by full-length mutant huntingtin, suggesting that in vitro fragment aggregation can act as a proxy for monitoring the disease-producing conformational property in HD. Thus, identification and testing of compounds that alter in vitro aggregation is a viable approach for defining potential therapeutic compounds that may act on the deleterious conformational property of full-length mutant huntingtin.

Inhibition of MHC II gene transcription by nitric oxide and antioxidants

MHC class II molecules are expressed on the surface of antigen presenting cells and are loaded with peptides processed from the phagosomal compartment of these cells. Such complexes interact with the CD4 positive T lymphocyte receptor for antigen and a strong interaction is followed by T cell activation and proliferation. As class II expression is critical for antigen specific immunity its expression mostly restricted to a few cell types but can be induced on others in response to interferon gamma. This expansion of antigen presenting ability plays a role in increasing the duration and intensity of the immune response. Nitric oxide and antioxidants attenuate this class II induction through negative effects on the induction of class II transactivator protein expression and on the binding of transcription factor NF-Y to the class II promoter.

Celastrol inhibits pro-inflammatory cytokine secretion in Crohn's disease biopsies

Crohn's disease is a chronic intestinal inflammatory process. In modern therapy, TNF-alpha inhibition is the main goal. The aim here is to characterize the effects of Celastrol, a pentacyclic-triterpene, on the secretion of inflammatory cytokines by LPS-activated human cells. Celastrol dose-dependently inhibited the secretion of all tested pro-inflammatory cytokines with IC(50) in the nanomolar range. Effect not related to glucocorticoid receptor activity is shown by competition experiments with the steroid antagonist RU486. Celastrol inhibited the pro-inflammatory cytokine secretion from mucosal inflammatory biopsies from Crohn's disease patients. Cytometry emphasized that for all tested pro-inflammatory cytokines, CD33(+) cells are the most sensitive. Quantitative-PCR and confocal analysis on a human monocytic cell line indicated that Celastrol acts at the transcriptional level by inhibiting LPS-induced NF-kappaB translocation. Celastrol might be a putative anti-inflammatory drug in the treatment of inflammatory diseases, given its inhibition of cytokine production by intestinal biopsies from Crohn's disease patients.

Celastrols as inducers of the heat shock response and cytoprotection

Alterations in protein folding and the regulation of conformational states have become increasingly important to the functionality of key molecules in signaling, cell growth, and cell death. Molecular chaperones, because of their properties in protein quality control, afford conformational flexibility to proteins and serve to integrate stress-signaling events that influence aging and a range of diseases including cancer, cystic fibrosis, amyloidoses, and neurodegenerative diseases. We describe here characteristics of celastrol, a quinone methide triterpene and an active component from Chinese herbal medicine identified in a screen of bioactive small molecules that activates the human heat shock response. From a structure/function examination, the celastrol structure is remarkably specific and activates heat shock transcription factor 1 (HSF1) with kinetics similar to those of heat stress, as determined by the induction of HSF1 DNA binding, hyperphosphorylation of HSF1, and expression of chaperone genes. Celastrol can activate heat shock gene transcription synergistically with other stresses and exhibits cytoprotection against subsequent exposures to other forms of lethal cell stress. These results suggest that celastrols exhibit promise as a new class of pharmacologically active regulators of the heat shock response.

Preparative isolation and purification of celastrol from Celastrus orbiculatus Thunb. by a new counter-current chromatography method with an upright coil planet centrifuge

A new counter-current chromatography (CCC) method with an upright coil planet centrifuge, which holds four identical multilayer coil columns in the symmetrical positions around the centrifuge axis, was applied to the isolation and purification of celastrol from the roots of Celastrus orbiculatus Thunb. The crude celastrol was obtained by elution with light petroleum from ethanol extracts using 15 cm x 5 cm i.d. silica gel flash chromatography. Preparative CCC with a two-phase system composed of light petroleum (bp 60-90 degrees C)-ethyl acetate-tetrachloromethane-methanol-water (1:1:8:6:1, v/v) was successfully performed, yielding 798 mg celastrol at 99.5% purity from 1020 mg of the crude sample in one step separation.

Medicinal chemistry approaches for the treatment and prevention of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia, which is characterised by progressive deterioration of memory and higher cortical functions that ultimately result in total degradation of intellectual and mental activities. Modern strategies in the search of new therapeutic approaches are based on the morphological and biochemical characteristics of AD, and focused on following directions: agents that compensate the hypofunction of cholinergic system, agents that interfere with the metabolism of beta-amyloid peptide, agents that protect nerve cells from toxic metabolites formed in neurodegenerative processes, agents that activate other neurotransmitter systems that indirectly compensate for the deficit of cholinergic functions, agents that affect the process of the formation of neurofibrillary tangles, anti-inflammatory agents that prevent the negative response of nerve cells to the pathological process. The goal of the present review is the validation and an analysis from the point of view of medicinal chemistry of the principles of the directed search of drugs for the treatment and prevention of AD and related neurodegenerative disorders. It is based on systematization of the data on biochemical and structural similarities in the interaction between physiologically active compounds and their biological targets related to the development of such pathologies. The main emphasis is on cholinomimetic, anti-amyloid and anti-metabolic agents, using the data that were published during the last 3 to 4 years, as well as the results of clinical trials presented on corresponding websites.

Regulating factors for microglial activation

Microglia, residential macrophages in the central nervous system, can release a variety of factors including cytokines, chemokines, etc. to regulate the communication among neuronal and other types of glial cells. Microglia play immunological roles in mechanisms underlying the phagocytosis of invading microorganisms and removal of dead or damaged cells. When microglia are hyperactivated due to a certain pathological imbalance, they may cause neuronal degeneration. Pathological activation of microglia has been reported in a wide range of conditions such as cerebral ischemia, Alzheimer's disease, prion diseases, multiple sclerosis, AIDS dementia, and others. Nearly 5000 papers on microglia can be retrieved on the Web site PubMed at present (November 2001) and half of them were published within the past 5 years. Although it is not possible to read each paper in detail, as many factors as possible affecting microglial functions in in vitro culture systems are presented in this review. The factors are separated into "activators" and "inhibitors," although it is difficult to classify many of them. An overview on these factors may help in the development of a new strategy for the treatment of various neurodegenerative diseases.

Scavenger receptor class B type I expression and elemental analysis in cerebellum and parietal cortex regions of the Alzheimer's disease brain

Metal ions play an important role in health and disease by influencing cellular biochemical pathways. The increased concentrations of some metal ions may have cytotoxic effects through their ability to oxidatively modify biomolecules, which may cause oxidative stress-induced brain cell death leading to neurodegenerative disorders observed in Alzheimer's disease (AD). We therefore performed elemental analysis of human brain tissues by a sophisticated method of inductively coupled plasma mass spectrometry (ICP-MS) in two regions of the AD brain, the parietal cortex and cerebellum, and compared them with the age-matched control. Our analysis shows the differential distribution of some metal ions in the two regions of the brain. Most importantly, Si, Sn, Al and Mn showed significantly higher levels in the parietal cortex of the AD brain compared to the control. The other metal ions showing moderate increases in the parietal cortex were Na, Te, Cr, Fe and B. Since these metal ions can modify lipoproteins in the brain and modified lipoproteins are taken up by scavenger receptors class B type I (SR-BI), we also determined the presence of SR-BI in the parietal cortex and cerebellum regions of the control and AD brains using a sensitive method, the reverse transcriptase-polymerase chain reaction. Our results suggest that SR-BI are present in the parietal cortex as well as in the cerebellum of the control and AD brains, suggesting that the presence of SR-BI may be involved in the uptake of oxidatively modified lipoproteins and beta-amyloid (Abeta) protein complexed with apoE, suggesting implications in the progression of late onset AD and other neurodegenerative disorders characterized by the deposition of insoluble aggregates observed in the AD brain.