Mariel Marder

Overview—Flavonoids: A New Family of Benzodiazepine Receptor Ligands

Benzodiazepines (BDZs) are the most widely prescribed class of psychoactive drugs in current therapeutic use, despite the important unwanted side-effects that they produce such as sedation, myorelaxation, ataxia, amnesia, ethanol and barbiturate potentiation and tolerance. Searching for safer BDZ-receptor (BDZ-R) ligands we have recently demonstrated the existence of a new family of ligands which have a flavonoid structure. First isolated from plants used as tranquilizers in folkloric medicine, some natural flavonoids have shown to possess a selective and relatively mild affinity for BDZ-Rs and a pharmacological profile compatible with a partial agonistic action. In a logical extension of this discovery various synthetic derivatives of those compounds, such as 6,3′-dinitroflavone were found to have a very potent anxiolytic effect not associated with myorelaxant, amnestic or sedative actions. This dinitro compound, in particular, exhibits a high affinity for the BDZ-Rs (Ki = 12–30 nM). Due to their selective pharmacological profile and low intrinsic efficacy at the BDZ-Rs, flavonoid derivatives, such as those described, could represent an improved therapeutic tool in the treatment of anxiety. In addition, several flavone derivatives may provide important leads for the development of potent and selective BDZ-Rs ligands.

6-Methylapigenin and hesperidin: new valeriana flavonoids with activity on the CNS

Valerian is an ancient tranquillizing drug obtained from the underground organs of several Valeriana species. Its active principles were assumed to be terpenoids in the form of valepotriates and/or as components of the essential oil. However, unknown active compounds were not discarded and synergic effects were suspected. We have recently isolated 6-methylapigenin (MA) from Valeriana wallichii and proved that it is a benzodiazepine binding site (BDZ-bs) ligand [Planta Med. 68 (2002) 934]. The present paper is the first report of the presence of 2S(-)-hesperidin in valeriana and describes that it has sedative and sleep-enhancing properties. MA, in turn, was found to have anxiolytic properties and was able to potentiate the sleep-enhancing properties of hesperidin (HN).MA and HN are new members of the growing family of natural flavonoids with activity on the CNS, and their properties suggest that they are promising drug leads in the field.

GABA(A)-receptor ligands of flavonoid structure.

This review describes the new research developments that have established the CNS-activity of some natural flavonoids. The properties of flavone, chrysin, apigenin and cirsiliol are described and a survey of the occurrence of ligands for the benzodiazepine binding site in the flavonoid field is attempted. Natural compounds, structurally related to flavonoids and with similar CNS-activities, are also included. A medicinal chemistry approach to improve the biochemical and pharmacological properties of the flavone nucleus is described alongside with the enumeration of the principal achievements obtained to date. Quantitative structure-activity relationships studies leading to the formulation of pharmacophore models presumably describing the characteristics of the flavone-binding site in the GABA(A)-receptor are summarized.

SEDATIVE AND SLEEP-ENHANCING PROPERTIES OF LINARIN, A FLAVONOID-ISOLATED FROM VALERIANA OFFICINALIS

We have recently reported the presence of the anxiolytic flavone 6-methylapigenin (MA) and of the sedative and sleep-enhancing flavanone glycoside 2S (-) hesperidin (HN) in Valeriana officinalis and Valeriana wallichii. MA, in turn, was able to potentiate the sleep-inducing properties of HN. The present paper reports the identification in V. officinalis of the flavone glycoside linarin (LN) and the discovery that it has, like HN, sedative and sleep-enhancing properties that are potentiated by simultaneous administration of valerenic acid (VA). These effects should be taken into account when considering the pharmacological actions of valeriana extracts.

Galectin-3 controls the response of microglial cells to limit cuprizone-induced demyelination

Galectin-3 (Gal-3) is a β-galactoside-binding lectin that plays an important role in inflammatory and neurodegenerative diseases. Cuprizone (CPZ)-induced demyelination is characterized by the loss of mature oligodendrocytes (OLG) by apoptosis, myelin sheath degeneration and recruitment of microglia and astrocytes to the lesioned area. We compared CPZ-induced demyelination of 8-week-old Lgals3(-/-) vs WT mice. Lgals3(-/-) mice displayed a similar susceptibility to CPZ-induced demyelination up to the fifth week, as evaluated by MBP immunostaining and electronic microscopy. However, OLG progenitors (OPC) generated in CPZ-treated Lgals3(-/-) mice showed diminished arborization, suggesting decreased ability of these cells to differentiate. Surprisingly, while WT mice experienced spontaneous remyelination in the fifth week of CPZ treatment-even though the CPZ diet was maintained up to sixth week-Lgals3(-/-) mice lacked this capacity and suffered continuous demyelination up to the sixth week, accompanied by pronounced astroglial activation. Moreover, after 2weeks of CPZ treatment, WT and Lgals3(-/-) mice showed lower innate anxiety as compared with respective naive mice, but only CPZ-treated Lgals3(-/-) mice showed decreased locomotor activity and exhibited spatial working memory impairment. Expression of Gal-3 increased during CPZ-induced demyelination in microglia but not in astrocytes. While CPZ-treated WT mice displayed heightened microglial activation associated with ED1 expression and pronounced upregulation of the phagocytic receptor TREM-2b, this effect was not observed in CPZ-treated Lgals3(-/-) mice which, in spite of showing an increased number of microglia, these cells evidenced caspase-3 activation. Our results indicate that Gal-3 is expressed in microglial cells to modulate their phenotype, facilitating the onset of remyelination and OLG differentiation.

Flavonoids as GABAA receptor ligands: the whole story?

Benzodiazepines are the most widely prescribed class of psychoactive drugs in current therapeutic use, despite the important unwanted side effects that they produce, such as sedation, myorelaxation, ataxia, amnesia, and ethanol and barbiturate potentiation and tolerance. They exert their therapeutic effects via binding to the benzodiazepine binding site of gamma-aminobutyric acid (GABA) type A receptors, and allosterically modulating the chloride flux through the ion channel complex. First isolated from plants used as tranquilizers in folkloric medicine, some natural flavonoids have been shown to possess selective affinity for the benzodiazepine binding site with a broad spectrum of central nervous system effects. Since the initial search for alternative benzodiazepine ligands amongst the flavonoids, a list of successful synthetic derivatives has been generated with enhanced activities. This review provides an update on research developments that have established the activity of natural and synthetic flavonoids on GABA type A receptors. Flavonoids are prominent drugs in the treatment of mental disorders, and can also be used as tools to study modulatory sites at GABA type A receptors and to develop GABA type A selective agents further.

Hesperidin, a flavonoid glycoside with sedative effect, decreases brain pERK1/2 levels in mice

The aim of this work was to evaluate if the intraperitoneal administration of the natural compound hesperidin, in a sedative dose, and neo-hesperidin, a hesperidin structural analog that exerts minor sedative effect, were able to induce changes in intracellular signaling cascades in different areas of the brain. The systemic administration of hesperidin produced a marked reduction in the phosphorylation state of extracellular signal-regulated kinases 1/2 (ERK 1/2), but not of Ca(+2)/calmodulin-dependent protein kinase II alpha subunit (alphaCaMKII), in the cerebral cortex, cerebellum and hippocampus. In contrast, neo-hesperidin did not markedly affect the activity of ERK 1/2 in both the cortex and the cerebellum. Taken together, these results demonstrated that intracellular signalling involving a selective decrease in ERK1/2 activation accompanied the depressant action of hesperidin. Even more, the low sedative action of neo-hesperidin correlates with a negligible decrease in phosphorylation state of ERK 1/2 (pERK 1/2), suggesting that low levels of pERK 1/2 in CNS could be a marker of sedative efficacy of flavonoids.

In vitro binding affinities of a series of flavonoids for μ-opioid receptors. Antinociceptive effect of the synthetic flavonoid 3,3-dibromoflavanone in mice.

The pharmacotherapy for the treatment of pain is an active area of investigation. There are effective drugs to treat this problem, but there is also a need to find alternative treatments free of undesirable side effects. In the present work the capacity of a series of flavonoids to bind to the μ opioid receptor was evaluated. The most active compound, 3,3-dibromoflavanone (31), a synthetic flavonoid, presented a significant inhibition of the binding of the selective μ opioid ligand [(3)H]DAMGO, with a Ki of 0.846 ± 0.263 μM. Flavanone 31 was further synthesized using a simple and cheap procedure with good yield. Its in vivo effects in mice, after acute treatments, were studied using antinociceptive and behavioral assays. It showed no sedative, anxiolytic, motor incoordination effects or inhibition of the gastrointestinal transit in mice at the doses tested. It evidenced antinociceptive activity on the acetic acid-induced nociception, hot plate and formalin tests (at 10 mg/kg and 30 mg/kg). The results showed that the 5-HT2 receptor and the adrenoceptors seem unlikely to be involved in its antinociceptive effects. Naltrexone, a nonselective opioid receptors antagonist, totally blocked compound 31 antinociceptive effects on the hot plate test, but naltrindole (δ opioid antagonist) and nor-binaltorphimine (κ opioid antagonist) did not. These findings demonstrated that 3,3-dibromoflavanone (31), at doses that did not interfere with the motor performance, exerted clear dose dependent antinociception when assessed in the chemical and thermal models of nociception in mice and it seems that its action is related to the activation of the μ opioid receptor.

6-Bromo-3'-nitroflavone, a new high affinity benzodiazepine receptor agonist recognizes two populations of cerebral cortical binding sites

Abstract The synthesis and biochemical characterization of 6-bromo-3′-nitroflavone ( 1 ) is presented. Compound 1 has higher affinity for cerebellar and cerebral cortical than for striatal, hippocampal, or spinal cord benzodiazepine receptors (BDZ-Rs). In the cerebral cortex it recognizes two populations of binding sites (K i s 1.2 nM and 15.5 nM, respectively), and at doses of 0.01 to 0.3 mg/kg, ip produces anxiolytic effects in mice.

Central nervous system activities of two diterpenes isolated from Aloysia virgata

Using the guide of a competitive assay for the benzodiazepine binding site in the γ-aminobutyric acid type A receptor (GABA(A)), two active diterpenes were isolated from the aerial parts of Aloysia virgata (Ruíz & Pavón) A.L. Jussieu var. platyphylla (Briquet) Moldenke. These compounds, identified as (16R)-16,17,18-trihydroxyphyllocladan-3-one (1) and (16R)-16,17-dihydroxyphyllocladan-3-one (2) on the basis of spectral data, competitively inhibited the binding of [(3)H]-FNZ to the benzodiazepine binding site with K(i)±S.E.M. values of 56±19 μM and 111±13 μM, respectively. The behavioral actions of these diterpenes, intraperitoneally (i.p.) administered in mice, were examined in the plus-maze, holeboard, locomotor activity and light/dark tests. Compound 1 exhibited anxiolytic-like effects in mice evidenced by a significant increase of the parameters measured in the holeboard test (the number of head dips at 0.3 mg/kg and 3 mg/kg, the rears at 1 mg/kg and the time spent head-dipping at 3 mg/kg), in the plus-maze assay (the percentage of open arm entries at 1 mg/kg) and in the light/dark test (the time in light and the number of transitions at 1 mg/kg). Compound 2 augmented the number of rearings in the holeboard apparatus (at 0.3 mg/kg and 1 mg/kg) and the locomotor activity (at 1 mg/kg). These results reveal the presence of neuroactive compounds in Aloysia virgata.