Multitarget neuroprotection by quercetin: Changes in gene expression in two perinatal asphyxia models

Hypoxic-ischemic encephalopathy (HIE) causes mortality and long-term neurologic morbidities in newborns, affecting pathways related to energy failure, excitotoxicity and oxidative stress that often lead to cell death. The whole process of HIE injury is coupled to changes in the expression of a great array of proteins. A nanoliposomal preparation of the flavonoid quercetin has been shown to exert neuroprotective effects in perinatal asphyxia models. This study aimed to identify neonatal HIE markers and explore the effect of quercetin administration in two perinatal asphyxia models: newborn rats and piglets. In the rat model, nanoliposomal quercetin administration reduced mortality after asphyxia. In the piglet model, quercetin partially overrode the reduction of HIF-1α mRNA levels in the cortex induced by asphyxia. Quercetin administration also reduced increased level of HO-1 mRNA in asphyctic piglets. These results suggest that quercetin neuroprotection might be involved in the regulation of HIF-1α, HO-1 and their targets. A proteomic approach revealed that the glycolytic pathway is strongly regulated by quercetin in both species. We also identified a set of proteins differentially expressed that could be further considered as markers. In piglets, this set includes Acidic Leucine-rich nuclear phosphoprotein 32 (ANP32A), associated with nervous system differentiation, proteins related with death pathways and alpha-enolase which can be converted to neuron-specific enolase, a glycolytic enzyme that may promote neuroprotection. In newborn rats, other promising proteins associated with neurogenesis and neuroprotection emerged, such as dihydropyrimidinase-related proteins, catalytic and regulatory subunits of phosphatases and heterogeneous nuclear ribonucleoprotein K (hnRNPK). Our results show that a nanoliposomal preparation of quercetin, with protective effect in two HIE mammal models, modulates the expression of proteins involved in energy metabolism and other putative neuroprotective signals in the cortex. Identification of these signals could reveal potential molecular pathways involved in disease onset and the novel quercetin neuroprotective strategy.

Intravenous nanosomes of quercetin improve brain function and hemodynamic instability after severe hypoxia in newborn piglets

Perinatal asphyxia is a major cause of death and neurological morbidity in newborns and oxidative stress is one of the critical mechanisms leading to permanent brain lesions in this pathology. In this context we have chosen quercetin, a natural antioxidant, known also by its brain protective effects to study its potential as a therapy for brain pathology provoked by severe hypoxia in the brain. To overcame the difficulties of quercetin to access the brain, we have developed lecithin/cholesterol/cyclodextrin nanosomes as a safe and protective vehicle. We have applied the nanosomal preparation intravenously to newborn piglets submitted to a severe hypoxic or ischemic/hypoxic episode and followed them for 8 or 72 h, respectively. Either towards the end of 8 h after hypoxia or up to 72 h after, electroencephalographic amplitude records in animals that received the nanosomes improved significantly. Animals receiving quercetin also stabilized blood pressure and recovered spontaneous breathing. In this experimental group mechanical ventilation assistance was withdrawn in the first 24 h while the hypoxic and vehicle groups required more than 24 h of mechanical ventilation. Three days after the hypoxia the suckling and walking capacity in the group that received quercetin recovered significantly compared with the hypoxic groups. Pathological studies did not show significant differences in the brain of newborn piglets treated with nanosomes compared with hypoxic groups. The beneficial effects of quercetin nanosomal preparation after experimental perinatal asphyxia show it as a promising putative treatment for the damaged brain in development.

Neuroprotective actions of flavones and flavonols: mechanisms and relationship to flavonoid structural features

Epidemiological studies have shown positive preventive action of flavonoids on cardiovascular and neurodegenerative events. Among the six groups in which flavonoids are classified, the flavones and flavonols, based on the backbone of 2-phenylchromen-4-one (2-phenyl-1-benzopyran-4-one) are the most commonly encountered within the families and genera of the higher plants. Numerous studies support a neuroprotective activity of flavones such as luteolin and flavonols such as kaempherol and quercetin in experimental focal ischemia and models of neurodegeneration. Antioxidation, modulation of signaling cascades and gene expression as well as anti-inflammation appear as the main protective mechanisms and mitochondria are a likely main target mediating the preventive actions against oxidative stress. Flavones and flavonols re-establish the redox regulation of proteins, transcription factors and signaling cascades that are otherwise inhibited by elevated oxidative stress. The final survival or death of the neuron depends on flavone and flavonol concentrations, time of exposure and, mainly, metabolic and oxidative neuronal circumstances. Neuroprotection appears to be linked to specific structural motifs, beyond those involved in antioxidation. By themselves or as templates for synthetic compounds, flavone and flavonol molecules show potential as multi-targeted therapeutic tools for protecting the brain. Nonetheless, more research needs to be done on the correlation of potential beneficial effects of flavones and flavonols and their mechanisms of action.

Life or death: neuroprotective and anticancer effects of quercetin

ETHNOPHARMACOLOGICAL RELEVANCE

Quercetin is a ubiquitous flavonoid that is present in numerous plants that are utilized in many different cultures for their nervous system and anticancer effects. To better understand the neuroprotective and antiproliferative activities of quercetin, we present a comprehensive review of the divergent actions that contribute to the ethnopharmacological profile of these plants.

RESULTS

The pharmacological activities of quercetin that modulate antioxidation/oxidation/kinase-signaling pathways might be differentially elicited in neurons compared with malignant cells, ultimately promoting cell survival or death in a cell type- and metabolism-specific manner. Whereas the broad antioxidation and anti-inflammatory activities of quercetin are important for neuronal survival, the oxidative, kinase- and cell cycle-inhibitory, apoptosis-inducing effects of quercetin are essential for its anticancer effects. The diverse mechanistic interactions and activities of quercetin that modulate the phosphorylation state of molecules as well as gene expression would alter the interconnected and concerted intracellular signaling equilibrium, either inhibiting or strengthening survival signals. These mechanisms, which have been mainly observed in in vitro studies, cannot be easily translated into an explanation of the divergent simultaneous neuroprotective and anticancer effects observed in vivo. This is in part due to low bioavailability in plasma and in the brain, as well as the nature of the actual active molecules.

CONCLUSIONS

Numerous studies have demonstrated the beneficial effects of chronic quercetin intake, which is ethnopharmacologically meaningful, as many plants that are chronically ingested by people contain quercetin. Although quercetin and quercetin-containing plants exhibit potential as therapeutic modalities in neuropathology and in cancer, the data collectively highlight the need to elucidate issues such as bioavailability as well as its correlation with effectiveness at biomarkers in vivo. There would be an increased potentential of these plants for chemoprevention and neuropathology prevention.

After cellular internalization, quercetin causes Nrf2 nuclear translocation, increases glutathione levels, and prevents neuronal death against an oxidative insult

In this work we describe the protective effects of quercetin against H(2)O(2) in 24-h-pretreated neuronal cultures. We explored quercetin availability and subcellular fate through the use of HPLC-Diode Array Detection (DAD), epifluorescence, and confocal microscopy. We focused on quercetin modulation of thiol-redox systems by evaluating changes in mitochondrial thioredoxin Trx2, the levels of total glutathione (GSH), and the expression of the gamma-glutamate-cysteine ligase catalytic subunit (GCLC), the rate-limiting enzyme of GSH synthesis, by the use of Western blot, HPLC, and real-time PCR techniques, respectively. We further explored the activation of the protective NF-E2-related factor 2 (Nrf2)-dependent signaling pathway by quercetin using immunocytochemistry techniques. Our results showed rapid quercetin internalization into neurons, reaching the nucleus after its addition to the culture. Quercetin pretreatment increased total GSH levels, but did not increase Trx2. Interestingly it caused Nrf2 nuclear translocation and significantly increased GCLC gene expression. At the moment of H(2)O(2) addition, intracellular quercetin or related metabolites were undetectable in the cultures although quercetin pretreatment prevented neuronal death from the oxidant exposure. Our findings suggest alternative mechanisms of quercetin neuroprotection beyond its long-established ROS scavenging properties, involving Nrf2-dependent modulation of the GSH redox system.

In silico characterization of cytisinoids docked into an acetylcholine binding protein

Homology models of nicotinic acetylcholine receptors (nAChRs) suggest that subtype specificity is due to non-conserved residues in the complementary subunit of the ligand-binding pocket. Cytisine and its derivatives generally show a strong preference for heteromeric alpha4beta2* nAChRs over the homomeric alpha7 subtype, and the structural modifications studied do not cause large changes in their nAChR subtype selectivity. In the present work we docked cytisine, N-methylcytisine, and several pyridone ring-substituted cytisinoids into the crystallographic structure of the Lymnaea stagnalis acetylcholine binding protein (AChBP) co-crystallized with nicotine (1UW6). The graphical analysis of the best poses showed that cytisinoids have weak interactions with the side chains of the non-conserved amino acids in the complementary subunit justifying the use of PDB 1UWB as a surrogate for nAChR. Furthermore, we found a high correlation (R(2)=0.96) between the experimental pIC(50) values at alpha4beta2* nAChR and docking energy (S) of the best cytisinoid poses within the AChBP. Due to the quality of the correlation we suggest that this equation might be used as a predictive model to propose new cytisine-derived nAChRs ligands. Our docking results also suggest that further structural modifications of these cytisinoids will not greatly alter their alpha4beta2*/alpha7 selectivity.

Pretreatment with natural flavones and neuronal cell survival after oxidative stress: a structure-activity relationship study

Quercetin shows structural features that have been related to the antioxidant potency of flavonoids and also shows neuroprotection in different models of oxidative death. Because only a few studies have focused on the flavonoid structural requirements for neuroprotection, this work evaluated the protective capacity of 13 flavones structurally related to quercetin, isolated from Kenyan plants, to rescue primary cerebellar granule neurons from death induced by a treatment with 24 h of hydrogen peroxide (150 microM). Each flavone (0-100 microM) was applied 24 h prior to the oxidative insult, and neuronal viability was evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Results suggest that the o-dihydroxy substitution in the B-ring is not necessary to afford neuroprotection and could be partly responsible for neurotoxic effects. Furthermore, the hydroxy substitutions in the positions C3 (C-ring) in C5 and C7 (A-ring) would be important for neuroprotection in this model.

Immunomodulatory properties of Achyrocline satureioides (Lam.) D.C. infusion: a study on human leukocytes

AIM OF THE STUDY

Achyrocline satureioides (Lam.) D.C. is a South American native medicinal herb known by the popular name of "Marcela". Its infusion is widely utilized for the treatment of several digestive ailments, as an anti-inflammatory preparation, as a sedative and anti-atherosclerotic. Circumstantial evidence suggests that extracts of Achyrocline satureioides may have immunomodulatory properties. The present study was therefore devised to investigate the in vitro effects Achyrocline satureioides infusion on human peripheral blood mononuclear cells (PBMCs) and polymorphonuclear leukocytes (PMNs).

MATERIALS AND METHODS

Experiments were performed on cells isolated from venous blood obtained from healthy donors. PBMC proliferation and cytokine production were assessed by standard ELISA methods. Reactive oxygen species (ROS) production by PMNs was evaluated by spectrofluorimetry.

RESULTS

In PBMCs, Achyrocline satureioides infusion in the 0.06-0.24microg/ml quercetin equivalent (QE) concentration range concentration-dependently reduced PHA-induced proliferation and production of interferon (IFN)-gamma and interleukin (IL)-4. Lower concentrations of the infusion (0.006-0.03microg/ml QE), which were ineffective on cell proliferation, significantly increased the production of both IFN-gamma and IL-4 and decreased the ratio IFN-gamma/IL-4. In PMNs, Achyrocline satureioides infusion slightly increased the spontaneous generation of ROS only at concentrations > or =0.06microg/ml QE. On the contrary, in the 0.0012-0.03microg/ml QE concentration range the infusion profoundly inhibited fMLP-induced ROS generation as well as spontaneous and fMLP-induced IL-8 production.

CONCLUSIONS

The present results provide evidence that Achyrocline satureioides infusion may exert several immunomodulatory effects, in line with its traditional use as an anti-inflammatory agent in many disease conditions. Further studies are warranted to better characterize such effects and to assess their therapeutic relevance.

Nicotine induces tyrosine hydroxylase plasticity in the neurodegenerating striatum

It has been shown that nicotine prevents the loss of dopamine (DA) in the corpus striatum (CS) after 6-hydroxydopamine injection in the substantia nigra. To study the role of the enzyme tyrosine hydroxylase (TH; EC 1.14.16.2) in this experimental paradigm, we have examined its activity by assessing the accumulation of l-3,4-dihydroxyphenylalanine after inhibiting the subsequent enzyme in the DA synthetic pathway, aromatic l-amino acid decarboxylase, with 3-hydroxybenzylhydrazine. In addition the amount of TH protein was assessed by western blotting and its distribution in the CS was examined using immunohistochemical methods. 6-hydroxydopamine injection produced a significant decrease in DA levels and l-3,4-dihydroxyphenylalanine accumulation, as well as decreases in TH protein and TH immunoreactive fibres in the CS. After nicotine treatment, the decrease in TH protein in the CS was significantly reduced, with a concomitant preservation of TH activity, but nicotine did not alter the number of TH immunoreactive fibres. The activity and amount of TH did not change in the contralateral (intact) CS. Thus, nicotine induces long lasting TH plasticity in the degenerating CS. A synergistic action of nicotine-activated and lesion-originated signals appears necessary for the expression of this neuronal molecular plasticity.

C3-halogenation of cytisine generates potent and efficacious nicotinic receptor agonists

Neuronal nicotinic acetylcholine receptors subserve predominantly modulatory roles in the brain, making them attractive therapeutic targets. Natural products provide key leads in the quest for nicotinic receptor subtype-selective compounds. Cytisine, found in Leguminosae spp., binds with high affinity to alpha4beta2* nicotinic receptors. We have compared the effect of C3 and C5 halogenation of cytisine and methylcytisine (MCy) on their interaction with native rat nicotinic receptors. 3-Bromocytisine (3-BrCy) and 3-iodocytisine (3-ICy) exhibited increased binding affinity (especially at alpha7 nicotinic receptors; Ki approximately 0.1 microM) and functional potency, whereas C5-halogenation was detrimental. 3-BrCy and 3-ICy were more potent than cytisine at evoking [3H]dopamine release from striatal slices (EC50 approximately 11 nM), [3H]noradrenaline release from hippocampal slices (EC50 approximately 250 nM), increases in intracellular Ca2+ in PC12 cells and inward currents in Xenopus oocytes expressing human alpha3beta4 nicotinic receptor (EC50 approximately 2 microM). These compounds were also more efficacious than cytisine. C3-halogenation of cytisine is proposed to stabilize the open conformation of the nicotinic receptor but does not enhance subtype selectivity.

From ligand design to therapeutic efficacy: the challenge for nicotinic receptor research

S-Nicotine, the principal psychoactive constituent of Nicotiana tabacum, underpins addiction to tobacco smoking. Although tobacco consumption is a leading cause of death worldwide, nicotine itself is also proposed to have potential therapeutic benefits for a diverse range of conditions. Nicotine interacts with its cognate receptors in the central nervous system to exert a predominantly modulatory influence, making neuronal nicotinic receptors attractive therapeutic targets. Here, we focus on three natural products as lead compounds for drug discovery programs, nicotine, epibatidine and cytisine, and consider the aims and limitations that shape these drug discovery endeavors.

Photoprotection by topical application of Achyrocline satureioides ('Marcela')

It has been demonstrated that the use of topical antioxidants can contribute to controling the free radicals excess produced by ultraviolet (UV) irradiation of the skin, being beneficial for processes such as photo aging and eventually cancer. Some plant extracts, particularly because of their polyphenolic constituents, can be beneficial for skin photo damage. Plant extracts of Achyrocline satureioides (AS) and Epilobium parviflorum (EP), potent antioxidant medicinal plants, were mixed with a cosmetic base and applied to the back skin of rabbits. Afterwards the skin was exposed to 1 h of UV irradiation from a known source. The production of the hydroxyl (OH.) radical was assessed in the skin after UV by measuring 2,3-dyhydroxybenzoic acid (2,3-DHBA), produced by the hydroxylation of sodium salicylate, previously injected intracutaneously (i.c.) in the irradiated areas. The UV provoked a marked increase in 2,3-DHBA that was significantly decreased by the AS cosmetic preparation. The EP extract did not show any effect on 2,3-DHBA production. It is concluded that the cosmetic preparation containing the AS extract is able to scavenge OH. production likely to be due to the presence of high concentrations of flavonoid aglycones such as quercetin, luteolin and 3-O-methylquercetin.

Cytoprotection by neutral fraction of tannat red wine against oxidative stress-induced cell death

Some of the beneficial effects of the Mediterranean diet on human pathologies have been attributed to red wine polyphenols. It has been postulated that the antioxidant activity of the latter would be also responsible for the cytoprotective capacity of red wine that has been reported in a few papers. Nevertheless, red wine shows a complex composition, and the active fraction is not known yet. In this context, the protective capacity of total lyophilized extracts of red wine and anthocyanin, neutral, or acidic fractions, was explored in PC12 cells in culture after a hydrogen peroxide insult. Although all fractions showed high antioxidant activity, only the neutral fraction was cytoprotective. The analysis of this active fraction showed that it was rich in the aglycons quercetin and myricetin as well as the glycosides of kaempferol, isorhamnetin, epicatechin, and catechin, some of which are known to be cytoprotective. This is the first paper to reveal the active fraction of total wine responsible of its cytoprotection.

Toxicological studies of the aqueous extract from Achyrocline satureioides (Lam.) DC (Marcela)

Achyrocline satureioides (Lam.) DC (Marcela) is known to possess a broad spectrum of pharmacological, medicinal and therapeutic properties. Previous studies have demonstrated various protective abilities of the marcela extracts against various pathological conditions. However, no extensive safety studies have been conducted on these extracts to date. In this paper, we evaluated the acute toxicity (dose levels of 30-300 mg/kg) of an aqueous extract of marcela, administered intraperitoneally and orally in mice and rats. The acute oral maximun tolerable dose in repeated administration during 4 h (1, 3 until 5 g/kg) was also studied in rats. The extract had low acute toxicity when administered intraperitoneally and no toxicity upon oral administration. The LD(50) of aqueous extracts of marcela was found to be greater than 5 g/kg when administered once via gastric intubation to rats. Weight gain, toxicity signs, enzymatic studies (transaminases and phosphatases) and histological evaluation of several organs indicated that the extract was devoid of acute toxicity. These acute studies demonstrated that an aqueous extract of marcela obtained after a 2% infusion is safe and did not cause any detrimental effects in vivo under the conditions investigated in this study.

Cytoprotection by Achyrocline satureioides (Lam) D.C. and some of its main flavonoids against oxidative stress

Epidemiological studies indicate that dietary antioxidants can influence the incidence of neurodegenerative diseases. Among them flavonoids have been proposed to be effective cytoprotectors. Consequently, herbs with a high concentration of these compounds such as Achyrocline satureioides, Ginkgo biloba and Epilobium parviflorum are of special interest. In this context a comparative study of the cytoprotective capacity of infusions from the three plants against an oxidative insult was performed. Hence, the cytoprotective activity of each infusion against H2O2 injury to PC12 cells was tested and the antioxidant capacity was assessed by the ABTS*+ radical bleaching assay. Free and glycosylated flavonoids contained in the infusions were identified by HPLC and the cytoprotective effect of some of these individual flavonoids was tested. The analysis of the flavonoid content of the infusions revealed different profiles. Epilobium parviflorum infusion showed the highest antioxidant capacity but only Achyrocline satureioides infusion proved to be cytoprotective. Moreover, the free flavonoids quercetin and luteolin contained in this infusion were also cytoprotective. In conclusion, the free radical scavenger capacity did not correlate with the cytoprotective profile of the infusions. The special mixture of unglycosylated Achyrocline satureioides flavonoids could be a clue to explain the unique effect of this plant.

Some aspects of the in vivo neuroprotective capacity of flavonoids: bioavailability and structure-activity relationship

On the basis of previous work showing that flavonoids structurally related to quercetin are neuroprotective for cells in culture, this work was directed towards determining if several flavonoids (quercetin, fisetin and catechin) could acutely and by an intraperitoneal (IP) route reach significant cerebral concentrations and either prevent or facilitate recovery from a brain lesion induced by focal ischemia in rats. Aqueous and liposomal preparations of quercetin, fisetin and catechin were administered IP in a single dose and assessed in the brain by HPLC at 30 min, 1 h, 2 h and 4 h. Ischemic damage from focal middle cerebral artery occlusion was assessed spectrophotometrically with 2,3,5,-triphenylltetrazolium chloride (TTC). Infarct volume was assessed by an image analysis system following perfusion with TTC. The status of the cerebral tissue was evaluated by hematoxylin-eosin. Flavonoids administered in aqueous preparations were undetected in the brain. Cerebral concentrations of catechin (10.5 ng/g), fisetin (8.23 ng/g) and quercetin (509 ng/g) were detected in the brain only after IP injection of the liposomal preparations. Spectrophotometric analysis of brain tissue with the TTC-technique showed that liposomal quercetin reduced ischemic damage and infarct volume after permanent occlusion of the middle cerebral artery (ischemic: 41.3 mm3 vs liposomal quercetin: 17 mm3). In liposomal quercetin-treated animals there was also recovery of the cytoarchitecture in ischemic areas of striatum and cortex. Although a liposomal preparation of fisetin had similar effects, catechin failed to protect brain tissue. In conclusion, early administration of liposomal preparations of quercetin and structurally related flavonoids are beneficial and neuroprotective in experimental focal ischemia.

Neuroprotection by flavonoids

The high morbidity, high socioeconomic costs and lack of specific treatments are key factors that define the relevance of brain pathology for human health and the importance of research on neuronal protective agents. Epidemiological studies have shown beneficial effects of flavonoids on arteriosclerosis-related pathology in general and neurodegeneration in particular. Flavonoids can protect the brain by their ability to modulate intracellular signals promoting cellular survival. Quercetin and structurally related flavonoids (myricetin, fisetin, luteolin) showed a marked cytoprotective capacity in in vitro experimental conditions in models of predominantly apoptotic death such as that induced by medium concentrations (200 M) of H2O2 added to PC12 cells in culture. Nevertheless, quercetin did not protect substantia nigra neurons in vivo from an oxidative insult (6-hydroxydopamine), probably due to difficulties in crossing the blood-brain barrier. On the other hand, treatment of permanent focal ischemia with a lecithin/quercetin preparation decreased lesion volume, showing that preparations that help to cross the blood-brain barrier may be critical for the expression of the effects of flavonoids on the brain. The hypothesis is advanced that a group of quercetin-related flavonoids could become lead molecules for the development of neuroprotective compounds with multitarget anti-ischemic effects.

Screening of antioxidant activity of three Indian medicinal plants, traditionally used for the management of neurodegenerative diseases

A number of Indian medicinal plants have been used for thousands of years in the traditional system of medicine (Ayurveda). Amongst these are plants used for the management of neurodegenerative diseases such as Parkinson's, Alzheimer's, loss of memory, degeneration of nerves and other neuronal disorders by the Ayurvedic practitioners. Though the etiology of neurodegenerative diseases remains enigmatic, there is evidence, which indicates that defective energy metabolism, excitotoxicity and oxidative damage may be crucial factors (Ann. Neurol. 38 (3) (1995) 357). The part of the Ayurvedic system that provides an approach to prevention and treatment of degenerative diseases is known as Rasayana, and plants used for this purpose are classed as rejuvenators. This group of plants generally possesses strong antioxidant activity (Pharmacol. Biochem. Behav. 43 (1992) 1175), but only a few have been investigated in detail. In the present study, three such rasayana plants were tested for the first time for their toxicity and free radical scavenging activity both in vitro and ex vivo. All the three plant infusions (up to 1 mg/ml) showed no toxic effects on the viability of PC12 cell line as judged by MTT-test. Both ethanolic extracts and water infusions of the plants were tested for their antioxidant activity in the 2,2'-azinobis-3-ethyl-benzothiazoline-6-sulfonic acid (ABTS*(+)) radical cation decolorization assay; inhibition of lipid peroxidation by plant infusions was carried out using spontaneous lipid peroxidation of rat brain homogenate, and IC50 values were determined. The results from the ABTS assay showed that the ethanolic extract of Sida cordifolia was found to be most potent (IC50 16.07 microg/ml), followed by Evolvulus alsinoides (IC50 33.39 microg/ml) and Cynodon dactylon (IC50 78.62 microg/ml). The relative antioxidant capacity for the water infusions was observed in the following order: E. alsinoides (IC50 172.25 microg/ml)>C. dactylon (IC50 273.64 microg/ml)>S. cordifolia (IC50 342.82 microg/ml). The results of water infusions of the plants on lipid peroxidation were as follows: E. alsinoides (IC50 89.23 microg/ml)>S. cordifolia) (IC50 126.78 microg/ml)>C. dactylon (IC50 608.31 microg/ml).

Cell culture protection and in vivo neuroprotective capacity of flavonoids

Flavonoids are an important group of recognized antioxidants ubiquitous in fruits, vegetables and herbs. There are epidemiological evidences for the stroke-protecting capacity of flavonoids and while the neuroprotective power of complex extracts rich in flavonoids like those of Ginkgo biloba, green tea or lyophilized red wine have been demonstrated in several studies, neuroprotection by individual flavonoids has been poorly studied in vivo. The neuroprotective capacity of individual flavonoids was studied in PC12 cells in culture and in a model of permanent focal ischemia (permanent Middle Cerebral Artery Occlusion - pMCAO). In the in vivo experiments, flavonoids were administered in lecithin preparations to facilitate the crossing of the blood brain barrier. The simultaneous incubation of PC12 cells with 200 micro M hydrogen peroxide (H2O2) and different flavonoids for 30 min resulted in a conspicuous profile: quercetin, fisetin, luteolin and myricetin significantly increased cell survival while catechin, kaempherol and taxifolin did not. Quercetin was detected in brain tissue 30 min and 1 h after intraperitoneal administration. When one of the protective flavonoids (quercetin) and one of those that failed to increase PC12 cell survival (catechin) were assessed for their protective capacity in the pMCAO model, administered i.p. 30 min after vessel occlusion, quercetin significantly decreased the brain ischemic lesion while catechin did not. It is concluded that when administered in liposomal preparations, flavonoids structurally related to quercetin could become leads for the development of a new generation of molecules to be clinically effective in human brain ischemia.

Presynaptic involvement in the nicotine prevention of the dopamine loss provoked by 6-OHDA administration in the substantia nigra

While nicotine, through stimulation of a specific sub-population of nicotinic acetylcholine receptors (nAChR) appears to protect cells in culture against a variety of insults, studies in vivo show controversial results. In a previous paper we have shown that in the 6-hydroxydopamine (6-OHDA) model of experimental parkinsonism, an intermittent administration schedule of nicotine (4 h before and 20, 44 and 68 h after 6-OHDA) was able to prevent the decrease of dopamine (DA) concentration in the corpus striatum (CS) provoked by the partial lesion of the substantia nigra (50% neuronal death after 6 micro g of 6-OHDA). To further analyze the mechanisms of nicotine effects, we performed a microdialysis study of striatal extracellular DA concentrations utilizing the nicotine administration schedule that was able to prevent DA decrease. Basal extracellular DA concentrations in the CS were maintained after 6-OHDA and were not modified by nicotine. Basal DOPAC levels were decreased after the neurotoxic administration. The response of extracellular DA to potassium chloride (KCl) challenge was significantly lower after 6-OHDA than in control animals. Nicotine significantly reversed this decrease. As previous studies have shown, the striatal DA terminals surviving the 6-OHDA toxic effect are able to keep extracellular DA concentrations close to normal, likely increasing DA synthesis. Nevertheless, the application of a releasing factor such as KCl shows the fragility of this equilibrium, exposing a decrease in the terminal number. Nicotine, through a further activation of tyrosine hydroxylase and DA synthesis or by prolonging the life of DA terminals, could reverse the effect of 6-OHDA.

Intracerebral administration of 2,4-diclorophenoxyacetic acid induces behavioral and neurochemical alterations in the rat brain

Although, the mechanism of 2,4-dichlorophenoxyacetic acid (2,4-D) neurotoxicity remains unknown, the monoaminergic system appears to mediate some of its effects in rats as we previously reported. In this study; we examined the 2,4-D effects on locomotor activity, circling behavior and monoamine levels after the injection into the basal ganglia of male adult rats. These effects were compared with those induced after selective lesions of dopaminergic neurons with 6-hydroxydopamine (6-OHDA). 2,4-D-injected into one striatum (100 microg/rat) produced a marked depression in locomotor activity and elicited a moderate circling towards the ipsilateral side at 6 and 24 h postinjection. These behavioral changes were accompanied by a decrease and an increase of serotonin (5-HT) and homovanillic acid (HVA) levels, respectively. 2,4-D administration (100 microg/rat) into the nucleus accumbens, induced similar behavioral and neurochemical patterns to the intrastriatal 2,4-D injection, although rats did not present notorious turning. When 2,4-D was injected into one medial forebrain bundle (MFB, 50 microg/rat), animals presented ipsilateral circling, while locomotor activity was unchanged at 3 and 7 days post-injection. These last rats also exhibited diminished levels of striatal 5-HT, dopamine (DA) and their metabolites without changes in the substantia nigra (SN). Animals sacrificed 3 and 7 days after a 6-OHDA injection into one of the MFB, presented progressive depletion of dopamine in striatum and SN. 2,4-D as well as 6-OHDA-treated rats into one of the MFB were challenged with low dose (0.05 mg/kg s.c.) of apomorphine (only at 7 days post-injection) to evaluate a possible DA-receptor supersensitivity. Only 6-OHDA treated rats showing a vigorous contralateral rotation activity. These results indicate that 2,4-D induced a regionally-specific neurotoxicity in the basal ganglia of rats. The neurotoxic effects of 2,4-D on basal ganglia by interacting with the monoaminergic system depended not only on the exact location of the 2,4-D injection, but also on the dose and time period of post-injection. Toxicity produced by 2,4-D appears to be different in monoaminergic terminals, axonal fibers, and cell bodies.

Nicotine prevents striatal dopamine loss produced by 6-hydroxydopamine lesion in the substantia nigra

While the work of several groups has shown the neuroprotective effects of nicotine in vitro, evidences for the same effects in vivo are controversial, mainly regarding neuroprotection in experimental models of Parkinson's disease. In this context, we investigated the capability of various systemic administration schedules of nicotine to prevent the loss of striatal dopamine levels produced by partial or extensive 6-hydroxydopamine (6-OHDA) lesion of rat substantia nigra (SN). Eight days after 6- and 10-microg injections of 6-OHDA in the SN there was a significant decrease of dopamine concentrations in the corpus striatum (CS) and a concomitant increase in dopamine turnover. While 10 microg 6-OHDA produced an almost complete depletion of dopamine in the SN, 6 microg decreased dopamine levels by 50%. Subcutaneous nicotine (1 mg/kg) administered 4 h before and 20, 44 and 68 h after 6 microg 6-OHDA, prevented significantly the striatal dopamine loss. Administered only 18 or 4 h before or only 20, 44 and 68 h after, nicotine failed to counteract the loss of dopamine or the increase in dopamine turnover observed in the CS. Nicotine also failed to prevent significantly the decrease of striatal dopamine levels produced by the 10-microg 6-OHDA intranigral dose. Chlorisondamine, a long-lasting nicotinic acetylcholine receptor antagonist, reverted significantly the nicotinic protective effects on dopamine concentrations. These results are showing that putative neuroprotective effects of nicotine in vivo depend on an acute intermittent administration schedule and on the extent of the brain lesion.

Do structural deviations between toxins adopting the same fold reflect functional differences?

Three-finger proteins form a structurally related family of compounds that exhibit a great variety of biological properties. To address the question of the prediction of functional areas on their surfaces, we tentatively conferred the acetylcholinesterase inhibitory activity of fasciculins on a short-chain curaremimetic toxin. For this purpose, we assimilated the three-dimensional structure of fasciculin 2 with the one of toxin alpha. This comparison revealed that the tips of the first and second loops, together with the C terminus residue, deviated most. A first recombinant fasciculin/toxin alpha chimera was designed by transferring loop 1 in its entirety together with the tip of loop 2 of fasciculin 2 into the toxin alpha scaffold. A second chimera (rChII) was obtained by adding the point Asn-61 --> Tyr substitution. Comparison of functional and structural properties of both chimeras show that rChII can accommodate the imposed modifications and displays nearly all the acetylcholinesterase-blocking activities of fasciculins. The three-dimensional structure of rChII demonstrates that rChII adopts a typical three-fingered fold with structural features of both parent toxins. Taken together, these results emphasize the great structural flexibility and functional adaptability of that fold and confirm that structural deviations between fasciculins and short-chain neurotoxins do indeed reflect functional diversity.

Evidence for a noncholinergic function of acetylcholinesterase during development of chicken retina as shown by fasciculin

Fasciculin 2 (FAS), an acetylcholinesterase (AChE) peripheral site ligand that inhibits mammalian AChE in the picomolar range and chicken AChE only at micromolar concentrations, was used in chick retinal cell cultures to evaluate the influence of AChE on neuronal development. The effects of other AChE inhibitors that bind the active and/or the peripheral site of the enzyme [paraoxon, eserine, or 1,5-bis(4-allyldimethylammoniumphenyl) pentan-3-one dibromide (BW284c51)] were also studied. Morphological changes of cultured neurons were observed with the drugs used and in the different cell culture systems studied. Cell aggregates size decreased by more than 35% in diameter after 9 days of FAS treatment, mainly due to reduction in the presumptive plexiform area of the aggregates. Eserine showed no effect on the morphology of the aggregates, although it fully inhibited the activity of AChE. In dense stationary cell culture, cluster formation increased after 3 days and 6 days of FAS treatment. However, FAS, at concentrations in which changes of morphological parameters were observed, did not inhibit the AChE activity as measured histochemically. In contrast, paraoxon treatment produced a slight morphological alteration of the cultures, while a strong inhibition of enzyme activity caused by this agent was observed. BW284c51 showed a harmful, probably toxic effect, also causing a slight AChE inhibition. It is suggested that the effect of an anticholinesterase agent on the morphological modifications of cultured neurons is not necessarily associated with the intensity of the AChE inhibition, especially in the case of FAS. Moreover, most of the effects of AChE on culture morphology appear to be independent of the cholinolytic activity of the enzyme. The results obtained demonstrate that FAS is not toxic for the cells and suggest that regions of the AChE molecule related to the enzyme peripheral site are likely to be involved with the nonclassical role of AChE.

Dopaminergic pharmacology and antioxidant properties of pukateine, a natural product lead for the design of agents increasing dopamine neurotransmission

The dopaminergic and antioxidant properties of pukateine [(R)-11-hydroxy-1,2-methylenedioxyaporphine, PUK], a natural aporphine derivative, were analyzed in the rat central nervous system. At dopamine (DA) D1 ([3H]-SCH 23390) and D2 ([3H]-raclopride) binding sites, PUK showed IC50 values in the submicromolar range (0.4 and 0.6 microM, respectively). When the uptake of tritiated dopamine was assayed by using a synaptosomal preparation, PUK showed an IC50 = 46 microM. In 6-hydroxydopamine unilaterally denervated rats, PUK (8 mg/kg but not 4 mg/kg) elicited a significant contralateral circling, a behavior classically associated with a dopaminergic agonist action. When perfused through a microdialysis probe inserted into the striatum, PUK (340 microM) induced a significant increase in dopamine levels. In vitro experiments with a crude rat brain mitochondrial suspension showed that PUK did not affect monoamine oxidase activities, at concentrations as high as 100 microM. PUK potently (IC50 = 15 microM) and dose-dependently inhibited the basal lipid peroxidation of a rat brain membrane preparation. As a whole, PUK showed a unique profile of action, comprising an increase in extracellular DA, an agonist-like interaction with DA receptors, and antioxidant activity. Thus, PUK may be taken as a lead compound for the development of novel therapeutic strategies for Parkinson disease.

Hydroxyl radical production in the substantia nigra after 6-hydroxydopamine and hypoxia-reoxygenation

To study the involvement of oxidative stress in 6-OHDA neurotoxicity, we investigated the production of the hydroxyl free radical (OH.) in the substantia nigra (SN) and the striatum (CS) several moments after intranigral injection of the neurotoxin, with or without an added episode of hypoxia (30 min, 95% N2, 5% O2). We utilized the hydroxylation of salicylate to 2,3 dihydroxybenzoic acid (2,3 DHBA) as indication of OH. production. When 2.3 DHBA levels were not modified, the levels of 2,5 DHBA were taken as an indication of cytochrome P450 (CYP 450) metabolism. 6-OHDA alone did not increase the production of 2,3 DHBA in the SN. 2,5 DHBA increased significantly after 120 min and was high up to 24 h. An episode of hypoxia (60 min after 6-OHDA injection) significantly worsened the decrease of dopamine (DA) in the striatum assessed 8 days after injection of 6-OHDA in the SN. Hypoxia performed 60 min and 24 h before or 24 h after 6-OHDA did not show any additional effect on striatal DA levels. Contrary to results obtained after 6-OHDA alone, 2,3 DHBA increased significantly 120 min after the injection, when the hypoxia-reoxygenation was added to the 6-OHDA treatment. Our data are showing a relationship between the increase in OH. production and a concomitant worsening of neuronal degeneration. As a whole, the results support the idea that neurons undergoing 6-OHDA neurotoxicity have their antioxidant defences affected and that oxidative stress is actually an important eliciting factor in 6-OHDA dependant neurodegeneration. However, OH. may not be the main radical species involved in this process. Additionally, 6-OHDA also appeared to provoke a long-term increase in CYP 450 activity.

Effects of alpha-erabutoxin, alpha-bungarotoxin, alpha-cobratoxin and fasciculin on the nicotine-evoked release of dopamine in the rat striatum in vivo

Snake neurotoxins (NTX) have proven to be valuable tools for the characterisation of muscular nicotinic acetylcholine receptor structure and function. It is very likely that they could also be utilised to identify subtypes of neuronal nicotinic receptors controlling specific functions within the central nervous system. In this study we examined the effects of long alpha NTX (alpha-bungarotoxin, alpha-Bgt, and alpha-cobratoxin, alpha-Cbt) and short alpha NTX (alpha-erabutoxin a, alpha-Ebt) as well as the anticholinesterase toxin fasciculin-2 (FAS), on the nicotine-evoked release of dopamine (DA) in the striatum, using the in vivo push-pull technique. The short toxins alpha-Ebt and FAS blocked the extracellular increase of DA evoked by nicotine at 4.2 microM concentrations and alpha-Ebt was more potent, as reflected by the blockade at the lower dose of 0.42 microM. In contrast, the long toxins showed a different profile of action. Alpha-Cbt did not show any blockade of the nicotine-evoked release of DA at the doses studied while alpha-Bgt did block it only at the higher dose (4.2 microM) These results indicate that short neurotoxins show a stronger interaction with striatal nicotinic receptors subtypes controlling DA release when compared to the long ones. This interaction of short neurotoxin polypeptides and presynaptic receptors may permit the further elucidation of the particular nicotinic receptor populations responsible for the modulation of striatal DA release.

Stable complexes involving acetylcholinesterase and amyloid-beta peptide change the biochemical properties of the enzyme and increase the neurotoxicity of Alzheimer's fibrils

Brain acetylcholinesterase (AChE) forms stable complexes with amyloid-beta peptide (Abeta) during its assembly into filaments, in agreement with its colocalization with the Abeta deposits of Alzheimer's brain. The association of the enzyme with nascent Abeta aggregates occurs as early as after 30 min of incubation. Analysis of the catalytic activity of the AChE incorporated into these complexes shows an anomalous behavior reminiscent of the AChE associated with senile plaques, which includes a resistance to low pH, high substrate concentrations, and lower sensitivity to AChE inhibitors. Furthermore, the toxicity of the AChE-amyloid complexes is higher than that of the Abeta aggregates alone. Thus, in addition to its possible role as a heterogeneous nucleator during amyloid formation, AChE, by forming such stable complexes, may increase the neurotoxicity of Abeta fibrils and thus may determine the selective neuronal loss observed in Alzheimer's brain.

Developmental regulation of mouse brain monomeric acetylcholinesterase

Acetylcholinesterase (AChE) molecular forms were studied during mouse brain development. Mouse embryos expressed a monomeric (G1) and a tetrameric (G4) AChE form. Our results indicate that G4 AChE expressed at embryonic day (ED) 9 and ED15 could be purified by acridinium-Sepharose chromatography and shared similar biochemical and kinetic properties with the adult form. However, the G1 form expressed at either embryonic stage did not bind to acridinium, was not inhibited by excess substrate, and possessed higher K(m) and lower Vmax values than the adult G1 form. Two peripheral anionic binding site inhibitors, fasciculin and propidium, had a significantly lower affinity for the monomeric form at ED9. Results are discussed in terms of the biological significance of the embryonic G1 form, and its resemblance to the AChE activity found, associated with the senile plaques present in the brains of Alzheimer's patients.

Acetylcholinesterase inhibitors block acetylcholine-evoked release of dopamine in rat striatum, in vivo

In the rat striatum, acetylcholine (ACh) increases dopamine (DA) release. The role of increased cholinergic activity provoked by acetylcholinesterase inhibitors (AChEi) on DA release is currently under revision after recent papers have shown a blockade of nicotinic transmission by AChEi in vitro. To study the effects of AChEi in vivo, Fasciculin2 (FAS), a peptidergic AChEi, and physostigmine (PHY), a classical carbamate AChEi, were applied through push-pull or microdialysis cannulae respectively, to the striatum of rats, alone or with ACh. Extracellular concentrations of DA were assessed by HPLC with electrochemical detection. Alone, the AChEi studied did not provoke changes in basal extracellular levels of DA, in the different doses studied. ACh (100 microM, 1 and 5 mM) applied through the push-pull cannulae in basal conditions provoked a dose-dependent increase of extracellular DA. This effect was not observed with ACh in concentrations of 100 microM and 1 mM if FAS (0.4 and 4.2 microM) was applied first. Higher concentrations of ACh (5 mM) evoked a partial response after FAS 0.42 microM, an effect still blocked by FAS at 4.2 microM. PHY 50 microM applied through microdialysis completely blocked the increase in DA release provoked by ACh 10, 20 mM, while at ACh 30 mM, PHY 50 microM only partially blocked the evoked increase. A partial blockade was also observed with PHY 20 microM, on the three different concentrations of ACh. On the other hand PHY 10 microM did not block any of the ACh doses perfused. These results showed that AChEi like FAS and PHY interfere with the ACh-evoked DA release in the striatum.

Neonatal acetylcholinesterase inhibition by fasciculin 2 in rats: a model for the study of central nervous system development?

Fasciculin 2 (FAS), a potent acetylcholinesterase (AChE, EC 3.1.1.7) inhibitory peptide with affinity for the enzyme in the nanomolar range was utilized together with two other AChE inhibitors (Paroxon and BW284c51) to study the role of AChE in central nervous system development. When drugs were intracisternally injected at postnatal days 3 and 5, only FAS showed a significant inhibition of hippocampus and striatum AChE (39% and 77% inhibition, respectively). After FAS treatment, animals showed convulsive behaviour which was blocked by subcutaneous pretreatment with atropine sulfate (10 mg/kg). An assessment of developmental indices showed no alteration in neurological reflex maturation, motor behaviour or cell morphology. Body weight gain was significantly lower only in FAS-treated animals compared to controls during the preweaning period. To investigate the specificity of this effect a synthetic loop of FAS (showing no activity in vitro or in vivo) and oxidized FAS (showing a weak inhibition in vitro and no activity in vivo) were also intracisternally injected. Animals injected with the loop showed normal body weight development while those treated with oxidized FAS showed impairment in body weight. In conclusion, FAS was the most potent drug at inhibiting neonatal AChE in vivo without nonspecific brain damage. Impairment in body weight seems to be dependent on AChE involvement, although the possibility of a direct FAS effect is discussed. These results point to FAS intracisternal treatment as a useful in vivo model to study the role of AChE in the critical period of early postnatal central nervous system development.

Apigenin, a component of Matricaria recutita flowers, is a central benzodiazepine receptors-ligand with anxiolytic effects

The dried flower heads of Matricaria recutita L. (Asteraceae) are used in folk medicine to prepare a spasmolytic and sedative tea. Our fractionation of the aqueous extract of this plant led to the detection of several fractions with significant affinity for the central benzodiazepine receptor and to the isolation and identification of 5,7,4'-trihydroxyflavone (apigenin) in one of them. Apigenin competitively inhibited the binding of flunitrazepam with a Ki of 4 microM and had no effect on muscarinic receptors, alpha 1-adrenoceptors, and on the binding of muscimol to GABAA receptors. Apigenin had a clear anxiolytic activity in mice in the elevated plusmaze without evidencing sedation or muscle relaxant effects at doses similar to those used for classical benzodiazepines and no anticonvulsant action was detected. However, a 10-fold increase in dosage produced a mild sedative effect since a 26% reduction in ambulatory locomotor activity and a 35% decrement in hole-board parameters were evident. The results reported in this paper demonstrate that apigenin is a ligand for the central benzodiazepine receptors exerting anxiolytic and slight sedative effects but not being anticonvulsant or myorelaxant.

Fasciculin inhibition of acetylcholinesterase is prevented by chemical modification of the enzyme at a peripheral site

Fasciculin 2 (FAS) is a 61 amino acid peptide present in Dendroaspis angusticeps snake venom, with a selective and potent inhibitory activity towards acetylcholinesterase (AChE). The specific interaction of FAS with peripheral sites present in Electrophorus electricus AChE (Ki = 0.04 nM FAS) was investigated by chemical modification with N,N-dimethyl-2-phenylaziridinium (DPA) in the presence of active or peripheral anionic site protective agents. An enzyme was obtained that compared to the native AChE is 10(6)-times less sensitive to FAS, is fully inhibited by edrophonium and tacrine, and is 25-170-times less sensitive to several peripheral site ligands. Characterization of catalytic functions showed that Km for acetylthiocholine was 4-fold lower in the DPA-modified enzyme, whereas Km for phenylacetate remained the same. Values for Kcat determined with both substrates were unchanged. Diminished catalytic efficiency reflects that hydrolysis and/or supply of cationic substrates to the active site was affected by DPA reaction at a peripheral site. Previous data implicate Trp-279 (Torpedo AChE sequence numbering) as the residue actually involved in DPA modification. Our results strongly support FAS binding to an AChE peripheral site which partially overlaps the site of other peripheral site ligands including acetylthiocholine.

Recovery of central noradrenergic neurons one year after the administration of the neurotoxin DSP4

The long-term effects of the systemic administration of DSP4 (N-(2-chloroethyl)N-ethyl-2-bromobenzylamine hydrochloride), a selective noradrenergic neurotoxin, on the endogenous levels of monoamines and their metabolites and on alpha- and beta-adrenoceptors in selected brain regions of the rat were examined. After 7 days, DSP4 caused a marked reduction (about 80%) of endogenous noradrenaline levels in locus coeruleus-innervated regions. At 90, 240 and 300 days after DSP4 injection, a partial and gradual recovery (50%, 41% and 25% of control values, respectively) of the noradrenaline cortical levels was evident. One year after DSP4 administration, brain regional noradrenaline stores were almost completely recovered. No changes in 5-hydroxytryptamine levels were observed in the three time intervals, but a mild decrease in cortical and hippocampal 5-hydroxyindolacetic acid levels was found 7 days after DSP4 injection. Following the profound noradrenaline depletion seen at 7 days, the cerebral cortical density of alpha 1-, alpha 2- and beta-adrenoceptors was significantly increased. Assessment of adrenergic receptors in cerebral cortex at 365 days after DSP4 injection, indicated that alpha 1- and alpha 2-adrenoceptor densities did not differ from control values; however, the density of beta-adrenoceptors remained increased. No changes were observed in the affinities of the three types of adrenoceptors studied. These results indicate that after a selective noradrenergic denervation induced by DSP4, there is a slow and gradual recovery of noradrenaline stores and of alpha 1- and alpha 2-adrenoceptor populations, suggesting a possible regrowth and/or collateral sprouting of noradrenergic terminals.

Monoamine oxidase inhibitory effects of some 4-aminophenethylamine derivatives

The in vitro and ex vivo monoamine oxidase (MAO) inhibitory effects of (+/-)4-dimethylamino-alpha-methyl-phenethylamine (4-DMAA) and (+/-)4-methylamino-alpha-methyl-phenethylamine (4-MAA) were reassessed, in comparison with the previously unstudied achiral parent compound, 4-dimethyl-aminophenethylamine (4-DMAPEA) and with a salt of 4-DMAA enriched in the levo isomer, ("-")-4-DMAA, using amiflamine [S-(+)-4-dimethylamino-alpha,2-dimethylphenethylamine] as positive control. The in vitro studies confirmed that 4-amino-alpha-methylphenethylamine derivatives are highly selective and reversible MAO-A inhibitors. Furthermore, ("-")-4DMAA was less active than the racemic mixture. The side chain-unsubstituted compound, 4-DMAPEA, proved to be a nonselective and reversible MAO inhibitor. The ex vivo results, in which catecholamines, serotonin (5-HT) and their metabolites were measured in two brain regions after i.p. administration, confirmed the results obtained in vitro. These results are consistent with the suggestion that the 4-amino group contributes to MAO inhibitory effects of alpha-methyl-phenethylamines, and show that the presence and orientation of an alpha-methyl side chain substituent may be important when determining the potency and selectivity of these compounds. All compounds tested could be quantified by HPLC with electrochemical detection.

Possible anxiolytic effects of chrysin, a central benzodiazepine receptor ligand isolated from Passiflora coerulea

The pharmacological effects of 5,7-dihydroxyflavone (chrysin), a naturally occurring monoflavonoid that displaces [3H]flunitrazepam binding to the central benzodiazepine (BDZ) receptors, were examined in mice. In the elevated plus-maze test of anxiety, diazepam (DZ, 0.3-0.6 mg/kg) or chrysin (1 mg/kg) induced increases in the number of entries into the open arms and in the time spent on the open arms, consistent with an anxiolytic action of both compounds. The effects of chrysin on the elevated plus-maze was abolished by pretreatment with the specific BDZ receptor antagonist Ro 15-1788 (3 mg/kg). In the holeboard, diazepam (1 mg/kg) and chrysin (3 mg/kg) increased the time spent head-dipping. In contrast, high doses of DZ (6 mg/kg) but not of chrysin produced a decrease in the number of head dips and in the time spent head-dipping. In the horizontal wire test, diazepam (6 mg/kg) had a myorelaxant action. In contrast, chrysin (0.6-30 mg/kg) produced no effects in this test. These data suggest that chrysin possesses anxiolytic actions without inducing sedation and muscle relaxation. We postulate that this natural monoflavonoid is a partial agonist of the central BDZ receptors.

4-Dimethylaminophenethylamine, a sensitive, specific, electrochemically detectable monoamine oxidase-B substrate

4-Dimethylaminophenethylamine (DMAPEA) was characterized as an MAO substrate. This compound was unaffected by MAO-A, while its oxidation by MAO-B was linear as a function of both time and enzyme concentration, with Km = 5.8 microM and Vmax = 21.2 pmol/min/mg protein, using a crude rat brain mitochondrial suspension as source of MAO. Both DMAPEA and its oxidation product, 4-dimethylaminophenylacetic acid (DMAPAA), can be detected electrochemically at 0.85 V. The high MAO-B affinity and selectivity of DMAPEA, together with its low oxidation potential, make this molecule a unique tool to determine MAO-B activity in a wide variety of tissue preparations using HPLC-ED.