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.

Chronic intraperitoneal and oral treatments with hesperidin induce central nervous system effects in mice.

Hesperidin (HN) is a flavanone glycoside abundantly found in citrus fruits. This flavonoid mediated central nervous system activity following intraperitoneal (i.p.) acute treatment. The responses of mice after the chronic i.p. (4 and 30 mg/kg/day) or the oral intake administration of this drug (20, 50 and 100 mg/kg/day) were studied by using the holeboard, the plus-maze and the locomotor activity tests. Hesperidin, chronically administered by the i.p. route, exerted a decrease in the locomotor and exploratory activities, thus evidencing a depressant activity. In turn, the chronic oral intake of this flavonoid induced anxiolytic-like effects. These varied responses could be attributed to the different routes of administration that could lead to the production of diverse active metabolites.

Hesperidin induces antinociceptive effect in mice and its aglycone, hesperetin, binds to µ-opioid receptor and inhibits GIRK1/2 currents.

This paper extended the evaluation of the depressant and antinociceptive activities of hesperidin in order to determine its effectiveness by the intraperitoneal and oral routes, its pharmacological interaction with diverse pathways of neurotransmission and the role of its aglycone, hesperetin. The capacity of hesperidin and hesperetin to bind to µ-opioid receptor and their actions on µ-opioid receptor co-expressed with GIRK1/GIRK2 channels (G protein-activated inwardly rectifying K+ channels) in Xenopus laevis oocytes were also determined. Hesperidin exhibited a depressant activity in the hole board and locomotor activity tests, antinociceptive activities in the abdominal writhing and hot plate tests and no motor incoordination in the inverted screen and rotarod assays, only by the intraperitoneal route. Hesperetin did not show any effects in vivo in mice in these models, but in vitro it displaced the [³H]DAMGO binding with low-affinity and inhibited inward currents through the expressed GIRK1/2 channels. Although hesperidin actions in vivo demonstrated to be mediated by an opioid mechanism of action, it failed to directly bind to and activate the µ-opioid receptor or produce any change on inward GIRK1/2 currents in vitro. However, it should be considered that hesperidin may be metabolized, possibly resulting in crucial changes in its biological activity.

Neuroactive flavonoid glycosides from Tilia petiolaris DC. extracts.

Pharmacological assay guided purification of an ethanol extract of Tilia petiolaris DC. inflorescences resulted in the isolation and identification of isoquercitrin (ISO), quercetin 3-O-glucoside-7-O-rhamnoside (QUE) and kaempferol 3-O-glucoside-7-O-rhamnoside (KAE). The behavioral actions of these glycosylated flavonoids were examined in the hole board, locomotor activity and thiopental-induced loss of righting reflex tests in mice. QUE (10 and 30 mg/kg) and KAE (30 mg/kg), intraperitoneally (i.p.) administered to mice, reduced all the parameters measured in the hole board test, but ISO (30 mg/kg) only reduced the number of rearings. Meanwhile QUE at 30 mg/kg i.p. also decreased the ambulatory locomotor activity and increased the sodium thiopental-induced time of loss of the righting reflex suggesting a clear depressant action. The above results demonstrate the occurrence of neuroactive flavonoid glycosides in Tilia.

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.

Opioid receptors are involved in the sedative and antinociceptive effects of hesperidin as well as in its potentiation with benzodiazepines.

Previous reports from our laboratory described the sedative activity of hesperidin (hesperetin-7-rhamnoglucoside). This property is greatly increased when the glycoside is injected jointly with diazepam and this interaction has been shown to be synergistic. In the present work the generality of the synergistic phenomenon is proved, since potentiation also occurs with several other benzodiazepines, namely alprazolam, bromazepam, midazolam and flunitrazepam. In order to advance in the study of the mechanism of action of hesperidin, the possible participation of several brain receptors, which are implicated in the control of numerous behavioral and physiological functions, was explored by investigating the effects of a variety of their antagonists on hesperidin actions. The results showed that the 5-HT2 receptor and the alpha1-adrenoceptor seem unlikely to be involved in the behavioral effects of hesperidin. Naltrexone, a nonselective antagonist of opioid receptors, totally blocked hesperidin effects on locomotion, and partially antagonized hesperidin-induced decreased exploration in the hole board test. Nor-binaltorphimine, a selective kappa opioid receptor antagonist, was able to partially block hesperidin effects on locomotor activity. Furthermore, hesperidin-induced antinociception was partially blocked by naltrexone, and potentiated by co-administration with alprazolam. Hence, the participation of the opioid system in the sedative, antinociceptive and potentianting effects of hesperidin with benzodiazepines in mice is highly probable. Our results suggest a possible beneficial use of the association of hesperidin with benzodiazepines, not only to improve human sedative therapy, but also in the management of pain.

Central nervous system depressant action of flavonoid glycosides.

The pharmacological effects on the central nervous system (CNS) of a range of available flavonoid glycosides were explored and compared to those of the glycosides 2S-hesperidin and linarin, recently isolated from valeriana. The glycosides 2S-neohesperidin, 2S-naringin, diosmin, gossipyn and rutin exerted a depressant action on the CNS of mice following i.p. injection, similar to that found with 2S-hesperidin and linarin. We demonstrate in this work that these behavioural actions, as measured in the hole board, thiopental induced sleeping time and locomotor activity tests, are unlikely to involve a direct action on gamma-aminobutyric acid type A (GABA(A)) receptors. The corresponding aglycones were inactive, pointing to the importance of the sugar moieties in the glycosides in their CNS depressant action following systemic administration. The pharmacological properties of the flavonoid glycosides studied here, in addition to our previous results with hesperidin and linarin, opens a promising new avenue of research in the field.