Gossypin-induced analgesia in mice

Apoptosis-Inducing Activity and Antiproliferative Effect of Gossypin on PC-3 Prostate Cancer Cells

AIM

The rapid growth, morbidity and mortality of prostate cancer, and the lack of effective treatment have attracted great interest of researchers to find novel cancer therapies aiming at the effect of gossypin on cell proliferation and apoptosis of PC-3 cells.

METHODS

The effect of gossypin on cell viability was determined using MTT assay at 5-100μg/ml and cisplatin (50μM) in a time-dependent manner in PC-3 cell lines. The expression levels of caspase-3 (CASP3) and caspase-9 (CASP9) for apoptosis and Nuclear Factor Kappa B (NFKB1) for survival, inflammation, and growth were evaluated by real-time PCR. Hoechst staining was used to analyze apoptosis.

RESULTS

Gossypin showed an anti-proliferative effect on PC3 cell line in a time- and dose-dependent manner. In addition, gossypin led to a significant increase in apoptosis genes (CASP3, CASP9) when compared to control while it caused a decrease in the level of NFKB1, which is accepted as apoptosis inhibitor (p<0.05) (cisplatin-like). Gossypin 50 and 100μM significantly induced apoptotic mechanism in PC-3 cells. However, no apoptotic or commonly stained nuclei have been observed in control group cells.

CONCLUSION

The results indicated that gossypin can be defined as a promising anticancer agent for PC-3 human prostate cancer cell line.

Antinociceptive effect of flavonol and a few structurally related dimethoxy flavonols in mice

Previous reports suggest flavonoids as potent analgesic compounds. Based on these observations, the present study investigated the antinociceptive action of flavonol, 3', 4'-dimethoxy flavonol, 6, 3'-dimethoxy flavonol, 7, 2'-dimethoxy flavonol, and 7, 3'-dimethoxy flavonol and the possible mechanisms involved in these effects. The antinociceptive effect of the investigated compounds in doses of 25, 50, 100, and 200 mg/kg was evaluated in male Swiss albino mice using the acetic acid test, formalin-induced nociception, and hot water tail immersion test. The role of opioid, tryptaminergic, adrenergic, dopaminergic, GABAergic, and K⁺_ATP channels in producing the antinociceptive effect was also studied using appropriate interacting agents. Treatment with flavonol and dimethoxy flavonols resulted in a significant reduction in the number of abdominal constrictions in the acetic acid test, a significant inhibition of the paw-licking/biting response time in both the phases of formalin nociception and also a significant increase in mean reaction time in the hot water tail immersion test. These observations revealed the antinociceptive effect of dimethoxy flavonols. The role of opioid, serotonergic (5HT₃), and dopaminergic system was identified in the antinociceptive effect of flavonol and all dimethoxy derivatives investigated. In addition, the role of GABAergic, K⁺_ATP channel, and α-2 adrenergic mechanisms were also observed in the antinociceptive action of some of the investigated compounds. The present study identified the antinociceptive effect of flavonol and dimethoxy flavonols in mice acting through different neuronal pathways.

Flavonoids and Their Biological Secrets

Flavonoids are tricyclic polyphenolic compounds naturally occurring in plants. Being nature’s antioxidants flavonoids have been shown to reduce the damages induced by oxidative stress in cells. Besides being an antioxidant, flavonols are demonstrated to have anti-infective properties, i.e., antiviral, antifungal, anti-angiogenic, anti-tumorigenic, and immunomodulatory bioproperties. Plants use them as one of their defense mechanisms against radiation-induced DNA damage and also for fungal infections. The use of flavonols for fabrication of new drugs has been underway with objectives to develop safer and effective therapeutic agents. This review covers 15 flavonols for their structure, biological properties, role in plant metabolisms, and current research focused on computational drug design using flavonols for searching drug leads.

Sedative-hypnotic like effect of 5-methoxyflavone in mice and investigation on possible mechanisms by in vivo and in silico methods

Flavonoids have been shown to possess central nervous system (CNS) depressant effect mediated through the ionotropic GABA_A receptors. In the present study, 5-methoxyflavone was evaluated for sedative-hypnotic like activity in mice and the mechanisms involved by employing a battery of tests including molecular docking studies. In the open field test, 5-methoxyflavone in various doses (50, 100 and 150 mg/kg, i.p) exhibited a significant and dose-dependent reduction in the spontaneous locomotor activity (F (530) = 87.17 P < 0.001). Pretreatment with 5-methoxyflavone decreased the latency to sleep induction after pentobarbitone or ether administration and also significantly increased the duration of sleep (p < 0.001). A significant and dose-dependent myorelaxant effect was observed with 5-methoxyflavone in the inclined plane, horizontal wire test and rota rod test. Pretreatment with picrotoxin, bicuculline, glycine, caffeine or NMDA either decreased or completely abolished the hypnotic effect of 5-methoxyflavone in mice. The above results revealed the involvement of GABA_A, adenosine, glycine and NMDA receptors in the hypnotic effect of 5-methoxyflavone. The results of in silico studies indicated that, 5-methoxyflavone exhibits good binding affinity towards these receptors by H-bond interactions. In conclusion, the present study identified a novel and potential sedative-hypnotic like effect of 5-methoxyflavone involving multiple mechanisms.

In Vivo Anti-Inflammatory and Analgesic Effects of Aqueous Extract of Cistus ladanifer L. From Morocco

This study is designed to evaluate the analgesic and anti-inflammatory activities of aqueous extract (AE) of Cistus ladanifer L. leaves in experimental animal models. The central analgesic activity of C. ladanifer AE is studied using hot plate method in rats, and the acute anti-Inflammatory activity of C. ladanifer is investigated by rats paw edema induced by subplantar injection of 0.5% carrageenan into the right hind paw. Rats are pretreated with AE of C. ladanifer at different doses (150, 175, and 200 mg/kg, i.p.). The tramadol and indomethacin are used as reference drugs for analgesic and anti-inflammatory studies, respectively. Our results show that the AE of C. ladanifer exhibited anti-inflammatory and analgesic effects dose dependent. In anti-inflammatory activity, the AE of C. ladanifer at all doses reduced significantly the edema paw inflammation after carrageenan injection. Furthermore at 200 mg/kg, the effect of AE is highly important than that of other doses. In addition, the same AE demonstrates significant analgesic effect in thermal-induced pain model. So, this activity is proved by significant reduction of pain score after administration of AE at all doses. The nociception protection effects in this case are, respectively, 70.3%, 74.55%, and 93.33% after administration of AE of C. ladanifer at doses 150, 175, and 200 mg/kg b.w. The results of our findings suggest that AE of C. ladanifer has potential analgesic and anti-inflammatory activities with evidence of possible involvement of peripheral and central effects in its actions.

Anti-nociceptive activity of a few structurally related trimethoxy flavones and possible mechanisms involved

BACKGROUND

The present study was designed to investigate the anti-nociceptive activity of a few structurally related trimethoxy flavones (7,2',3'-TMF, 7,2',4'-TMF, 7,3',4'-TMF and 7,5,4'-TMF) and the possible mechanisms involved.

METHODS

Anti-nociceptive activity was evaluated in mice by employing acetic acid-induced writhing, formalin-induced nociception and hot water tail immersion methods. The involvement of opioid, GABAergic, tryptaminergic, adrenergic and dopaminergic mechanisms and K+ATP channels in the anti-nociceptive activity of trimethoxy flavones was investigated using suitable interacting chemicals.

RESULTS

Trimethoxy flavones exhibited a significant and dose-dependent inhibition of acetic acid writhing. The paw-licking response time was reduced both in the early and late phases of formalin nociception in a dose-dependent manner by trimethoxy flavones. A significant increase in tail withdrawal latency time was also observed after trimethoxy flavones treatment. These observations revealed the potential anti-nociceptive action of the investigated trimethoxy flavones. Pretreatment with naloxone and bicuculline significantly attenuated the reduction of abdominal constrictions produced by all the tested trimethoxy flavones indicating a definite role of opioid and GABAergic mechanisms in the anti-nociceptive effect of trimethoxy flavones. The anti-nociceptive action elicited by various trimethoxy flavones was differently modulated by glibenclamide, ondansetron, yohimbine and sulpiride.

CONCLUSIONS

The investigated trimethoxy flavones exhibited promising anti-nociceptive activity in various nociceptive models, and multiple mechanisms are involved in the anti-nociceptive activity of these compounds.

Natural Flavonoids as Promising Analgesic Candidates: A Systematic Review

Due to the chemical structural diversity and various analgesic mechanisms, an increasing number of studies indicated that some flavonoids from medicinal plants could be promising candidates for new natural analgesic drugs, which attract high interests of advanced users and academic researchers. The aim of this systematic review is to report flavonoids and its derivatives as new analgesic candidates based on the pharmacological evidences. Sixty-four papers were found concerning the potential analgesic activity of 46 flavonoids. In this case, the evidence for analgesic activity of flavonoids and total flavonoids was investigated. Meanwhile, the corresponding analgesic mechanism of flavonoids was discussed by generalizing and analyzing the current publications. Based on this review, the conclusion can be drawn that some flavonoids are promising candidates for painful conditions and deserve particular attention in further research and development.

Immature spinal cord neurons are dynamic regulators of adult nociceptive sensitivity

Chronic pain is a debilitating condition with unknown mechanism. Nociceptive sensitivity may be regulated by genetic factors, some of which have been separately linked to neuronal progenitor cells and neuronal differentiation. This suggests that genetic factors that interfere with neuronal differentiation may contribute to a chronic increase in nociceptive sensitivity, by extending the immature, hyperexcitable stage of spinal cord neurons. Although adult rodent spinal cord neurogenesis was previously demonstrated, the fate of these progenitor cells is unknown. Here, we show that peripheral nerve injury in adult rats induces extensive spinal cord neurogenesis and a long-term increase in the number of spinal cord laminae I–II neurons ipsilateral to injury. The production and maturation of these new neurons correlates with the time course and modulation of nociceptive behaviour, and transiently mimics the cellular and behavioural conditions present in genetically modified animal models of chronic pain. This suggests that the number of immature neurons present at any time in the spinal cord dorsal horns contributes to the regulation of nociceptive sensitivity. The continuous turnover of these neurons, which can fluctuate between normal and injured states, is a dynamic regulator of nociceptive sensitivity. In support of this hypothesis, we find that promoters of neuronal differentiation inhibit, while promoters of neurogenesis increase long-term nociception. TrkB agonists, well-known promoters of nociception in the short-term, significantly inhibit long-term nociception by promoting the differentiation of newly produced immature neurons. These findings suggest that promoters of neuronal differentiation may be used to alleviate chronic pain.

Antinociceptive effect of certain dimethoxy flavones in mice

The aim of the present study was to evaluate the antinociceptive action of certain dimethoxy flavones (DMF, (7,2׳-dimethoxy flavone, 7,3׳-dimethoxy flavone, 7,4׳-dimethoxy flavone and 7,8,-dimethoxy flavone) and the possible mechanisms involved. The antinociceptive effect of dimethoxy flavones was investigated in mice employing acetic acid-induced abdominal writhings, formalin-induced nociception and hot water tail immersion assay procedures. To identify the possible mechanisms involved in the antinociceptive action of these compounds, acetic acid-induced abdominal constriction assay alone was employed. Mice were pretreated with naloxone, yohimbine, ondansetron, haloperidol, bicuculline or glibenclamide before dimethoxy flavone treatment to identify the role of opioid, adrenergic, 5HT3-serotonergic, dopaminergic, gamma-amino butyric acid (GABA) receptor or potassium channels, respectively. The investigated dimethoxy flavones produced a significant reduction in the number of abdominal constrictions in acetic acid assay. A dose dependent decrease in paw-licking response time was evident in both the early and late phases of formalin induced nociception. A significant increase in reaction time was also evident after treatment with various dimethoxy flavones in hot water tail immersion assay. Pretreatment with naloxone, ondansetron or glibenclamide significantly attenuated the antinociceptive effect of all the four dimethoxy flavones. Yohimbine pretreatment attenuated the antinociceptive response of 7,3׳-dimethoxy flavone, 7,4׳-dimethoxy flavone and 7,8-dimethoxy flavone. Pretreatment with haloperidol potentiated the antinociceptive response of all the tested dimethoxy flavones. The antinociceptive effect of 7,2׳-dimethoxy flavone and 7,3׳-dimethoxy flavone was annulled by bicuculline pretreatment. The results of the present study reveal the antinociceptive effect of dimethoxy flavones involving multiple pathways.

Anxiolytic-like and antinociceptive effects of 2(S)-neoponcirin in mice

Study aims: 2(S)-neopincirin (NEO) is a constituent from of Clinopodium mexicanum, which is used in traditional Mexican herbal medicine for its tranquilizing and analgesic properties. This study investigated the anxiolytic-like, sedative and antinociceptive effects of NEO in several mice models. Material and methods: The anxiolytic-like effect was evaluated in the hole-board (HBT) and Open Field Tests (OFT); sedative effect was evaluated in sleeping time induced by sodium pentobarbital, and its antinociceptive actions were measured in the hot plate test. To evaluate if the GABA receptor could be involved in the anxiolytic-like effect produced by NEO, in independent experiments, the effects produced by co-administration of NEO plus muscimol (MUS) and NEO plus Pitrotoxin (PTX) were evaluated in the HBT. Results: NEO was isolated from Clinopodium mexicanum leaves. The NMR, MS and optic rotation data helped establish its identity as (2S)-5-hydroxy-4′-methoxyflavanone-7-O-{β-glucopyranosyl-(1→6)-β-rhamnoside}. NEO showed an anxiolytic-like effect and was able to counter the nociception induced by a thermal stimulus in a dose-dependent manner. PTX blocked the anxiolytic-like effect of NEO, while MUS was able to enhance it. Conclusions: The findings of present work demonstrated that NEO possesses anxiolytic-like and antinociceptive effects in mice. Such effects are not associated with changes in the locomotor activity. These results supported the notion that anxiolytic-like effect of NEO involves the participation of GABAergic system.

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.

Analgesic effects of a standardized bioflavonoid composition from Scutellaria baicalensis and Acacia catechu

Anti-inflammatory properties of both baicalin and catechins have been widely reported. However, the reports of analgesic effects of baicalin and catechins are limited. Three commonly used pain-related animal models were employed to evaluate the analgesic activity of UP446, a standardized bioflavonoid composition of baicalin and catechins. Carrageenan-induced paw edema, formalin test, and abdominal constriction assays were used to evaluate antinociceptive activity of 150 mg/kg or 100 mg/kg oral doses of UP446. Ibuprofen was used as a reference compound in each test. Pretreatment of carrageenan-induced hyperalgesic animals with UP446 at 150 mg/kg oral dosage reduced the hypersensitivity of pain by 39.5%. Similarly, a single dose of UP446, given orally at 100 mg/kg, exhibited 58% and 71.9% inhibition in pain sensitivity compared to vehicle-treated control in writhing and formalin tests, respectively. These findings suggest that the standardized anti-inflammatory bioflavonoid composition, UP446, could also be employed to inhibit nociception.

Naringin directly activates inwardly rectifying potassium channels at an overlapping binding site to tertiapin-Q

BACKGROUND

G protein-coupled inwardly rectifying potassium (K(IR) 3) channels are important proteins that regulate numerous physiological processes including excitatory responses in the CNS and the control of heart rate. Flavonoids have been shown to have significant health benefits and are a diverse source of compounds for identifying agents with novel mechanisms of action.

EXPERIMENTAL APPROACH

The flavonoid glycoside, naringin, was evaluated on recombinant human K(IR) 3.1-3.4 and K(IR) 3.1-3.2 expressed in Xenopus oocytes using two-electrode voltage clamp methods. In addition, we evaluated the activity of naringin alone and in the presence of the K(IR) 3 channel blocker tertiapin-Q (0.5 nM, 1 nM and 3 nM) at recombinant K(IR) 3.1-3.4 channels. Site-directed mutagenesis was used to identify amino acids within the M1-M2 loop of the K(IR) 3.1(F137S) mutant channel important for naringin's activity.

KEY RESULTS

Naringin (100 µM) had minimal effect on uninjected oocytes but activated K(IR) 3.1-3.4 and K(IR) 3.1-3.2 channels. The activation by naringin of K(IR) 3.1-3.4 channels was inhibited by tertiapin-Q in a competitive manner. An alanine-scan performed on the K(IR) 3.1(F137S) mutant channel, replacing one by one aromatic amino acids within the M1-M2 loop, identified tyrosines 148 and 150 to be significantly contributing to the affinity of naringin as these mutations reduced the activity of naringin by 20- and 40-fold respectively.

CONCLUSIONS AND IMPLICATIONS

These results show that naringin is a direct activator of K(IR) 3 channels and that tertiapin-Q shares an overlapping binding site on the K(IR) 3.1-3.4. This is the first example of a ligand that activates K(IR) 3 channels by binding to the extracellular M1-M2 linker of the channel.

Oral supplementation of gossypin during lead exposure protects alteration in heme synthesis pathway and brain oxidative stress in rats

OBJECTIVE

The objective was to study the efficacy of oral supplementation of gossypin, a flavonoid, during lead exposure in preventive alterations in the heme synthesis pathway, brain oxidation, and tissue lead uptake in rats.

METHODS

Male rats were used for the experiment and were exposed to lead (0.5% in drinking water) or lead plus oral supplementation of gossypin (25 or 100mg/kg) for 3 wk to determine the preventive effect of gossypin against lead toxicity. Animals were sacrificed after 3 wk for various biochemical variables suggestive of oxidative stress and heme synthesis pathway in addition to the concentration of lead in the blood and brain.

RESULTS

Exposure to lead produced significant inhibition in the activity of blood delta-aminolevulinic acid dehydratase accompanied by an increase in urinary delta-aminolevulinic acid and the levels of reactive oxygen species. There were significant alterations in the levels of glutathione, thiobarbituric acid-reactive substances, reactive oxygen species, and superoxide dismutase activity on lead exposure. Most of these alterations were significantly prevented by oral coadministration of gossypin, particularly at the dose of 100mg/kg.

CONCLUSION

The antioxidant and moderate chelating properties of oral gossypin suggest a promising role in use either as a nutritional supplement during lead exposure or as a complementary chelating agent during chelation therapy.

Utilizing nature as a source of new probes for opioid pharmacology

Background: Traditional and current opioid pharmacology is fundamentally based on interactions between opioid receptors and compounds isolated from natural sources. Adverse effects associated with opioids have led to the search for compounds with diminished side effects. Discussion: Recent discoveries of non-nitrogenous and structurally diverse alkaloids as novel opioid ligands have led to renewed interest in the development of novel chemotypes for opioid receptors. Conclusion: The strong history of natural products as opioid receptor ligands suggests that nature is one of the most promising for the identification of novel opioids. This review highlights the vast potential of investigating natural products as novel probes of opioid receptors.

Reversal of LPS-induced central and peripheral hyperalgesia by green tea extract

Tea has recently attracted a great deal of attention for its beneficial health effects. Green tea polyphenols inhibit the production of arachidonic acid metabolites and leukotrienes resulting in decreased inflammatory responses. In the present study, the effect of green tea extract (GTE) on lipopolysaccharide (LPS)-induced thermal and behavioural hyperalgesia in mice and the possible involvement of the cyclooxygenase pathway in this paradigm was evaluated. GTE (25 mg/kg, i.p.), nimesulide (2 mg/kg, i.p.) and rofecoxib (2 mg/kg, i.p.) significantly attenuated LPS-induced thermal and behavioural hyperalgesia but per se did not modify any of the behavioural effects. Concurrent administration of a subeffective dose of GTE (10 mg/kg, i.p.) and rofecoxib (2 mg/kg, i.p.) or nimesulide (2 mg/kg, i.p.) significantly potentiated the antinociceptive effect of GTE in both LPS-induced thermal and behavioural hyperalgesia with nimesulide showing a more pronounced enhancing effect. Thus it can be concluded that GTE attenuates LPS-induced central and peripheral hyperalgesia by selective inhibition of cyclooxygenase-2 enzyme.

Gossypin protects primary cultured rat cortical cells from oxidative stress- and β-amyloid-lnduced toxicity

The present study investigated the effects of gossypin, 3,3',4',5,7,8-hexahydroxyflavone 8-glucoside, on the toxicity induced by oxidative stress or beta-amyloid (Abeta) in primary cultured rat cortical cells. The antioxidant properties of gossypin were also evaluated by cell-free assays. Gossypin was found to inhibit the oxidative neuronal damage induced by xanthine/xanthine oxidase or by a glutathione depleting agent, D,L-buthionine (S,R)-sulfoximine. In addition, gossypin significantly attenuated the neurotoxicity induced by Abeta(25-35). Furthermore, gossypin dramatically inhibited lipid peroxidation initiated by Fe2+ and ascorbic acid in rat brain homogenates. It also exhibited potent radical scavenging activity generated from 1,1-diphenyl-2-picrylhydrazyl. These results indicate that gossypin exerts neuroprotective effects in the cultured cortical cells by inhibiting oxidative stress- and Abeta-induced toxicity, and that the antioxidant properties of gossypin may contribute to its neuroprotective actions.

Quercetin, a bioflavonoid, attenuates thermal hyperalgesia in a mouse model of diabetic neuropathic pain

Diabetic neuropathic pain, an important microvascular complication in diabetes mellitus, has been recognised as one of the most difficult types of pain to treat. Lack of understanding of etiology involved, inadequate relief, development of tolerance and potential toxicity of classical antinociceptives warrant the investigation of newer agents to relieve pain. The aim of the present study was to explore the antinociceptive effect of a bioflavonoid, quercetin, both in control and streptozotocin (STZ)-induced diabetic mice. After 4 weeks of a single intraperitoneal injection of STZ (200 mg/kg), both control and diabetic mice were subjected to test thermal hyperalgesia by tail-immersion assay (warm water). Diabetic mice exhibited a significant hyperalgesia as compared with control mice. Quercetin (100 but not 50 mg/kg p.o.) produced a marked increase in tail-flick latencies in both diabetic and nondiabetic mice. Quercetin-induced increase in nociceptive threshold was reversed by naloxone (2 mg/kg i.p.), an opioid receptor antagonist. These preliminary results indicate an antinociceptive activity of quercetin, probably through modulation of opioidergic mechanism and point towards its potential to attenuate diabetic neuropathic pain.

5,7-Dihydroxy-6-methoxyflavone, a benzodiazepine site ligand isolated from Scutellaria baicalensis Georgi, with selective antagonistic properties

As part of an effort to identify naturally occurring GABA(A) receptor benzodiazepine binding site (BDS) ligands from traditional medicinal herbs, we previously reported that flavonoid derivatives isolated from Scutellaria baicalensis (S. baicalensis) Georgi exhibited significant affinities for the BDS. The present study describes the characterization of 5,7-dihydroxy-6-methoxyflavone (oroxylin A), one of the major components of the herbal extract. Oroxylin A inhibited [3H]flunitrazepam binding to rat cerebral cortical membrane with a IC(50) value of 1.09+/-0.07 microM. A GABA ratio of 1.09+/-0.04 suggests that oroxylin A interacts as an antagonist at the recognition site. In neuropharmacological studies, oral administration of oroxylin A (3.75-60 mg kg(-1)) did not result in significant changes in animal models routinely employed for benzodiazepine (BD) evaluation. However, oroxylin A selectively abolished the anxiolytic, myorelaxant and motor incoordination, but not the sedative and anticonvulsant effects elicited by diazepam, a BDS agonist. These results add oroxylin A to the list of CNS active flavonoids, and as the first naturally occurring member endowed with selective antagonistic actions via the BDS.

Antinociceptive activity ofSempervivum tectorum L. extract in rats

The extract of Sempervivum tectorum L. (Crassulaceae) containing several flavonoids is widely used as an antiinflammatory agent in folk medicine. Previous studies have demonstrated that various flavonoids or flavonoid-containing plant extracts produce significant antinociception, but no data are available concerning their antinociceptive effect especially at the spinal level. The purpose of the present study was to investigate the antinociceptive activity of Sempervivum tectorum L. extract on acute and inflammatory pain sensitivity in awake rats. The pain sensitivity was assessed by the acute tail- flick test in intact rats and by the paw withdrawal test after carrageenan-induced inflammation using heat stimulus. The plant extract was administered intraperitoneally and intrathecally in rats. The intraperitoneal injection of a high dose of the extract (1000 mg/kg) significantly (p < 0.05) increased the paw withdrawal latency of the inflamed paw. The intrathecal administration (30-300 micro g) caused a small, but significant increase (10%-15%) in tail- flick latency. In the carrageenan-induced inflammatory model, the intrathecally applied extract (30-1000 micro g) significantly decreased, but did not relieve the thermal hyperalgesia. The results suggest that the spinal cord does not seem to play an important role in the antinociceptive effects of this plant extract.

Advances in flavonoid research since 1992

Some of the recent advances in flavonoid research are reviewed. The role of anthocyanins and flavones in providing stable blue flower colours in the angiosperms is outlined. The contribution of leaf flavonoids to UV-B protection in plants is critically discussed. Advances in understanding the part played by flavonoids in warding off microbial infection and protecting plants from herbivory are described. The biological properties of flavonoids are considered in an evaluation of the medicinal and nutritional values of these compounds.

Naturally occurring antinociceptive substances from plants

Despite the progress that has occurred in recent years in the development of therapy, there is still a need for effective and potent analgesics, especially for the treatment of chronic pain. One of the most important analgesic drugs employed in clinical practice today continues to be the alkaloid morphine. In this review, emphasis will be given to the important contribution and the history of Papaver somniferum, Salix species, Capsicum species and Cannabis sativa in the development of new analgesics and their importance in the understanding of the complex pathways related to electrophysiological and molecular mechanisms associated with pain transmission. Recently discovered antinociceptive substances include alkaloids, terpenoids and flavonoid. Plant-derived substances have, and will certainly continue to have, a relevant place in the process of drug discovery, particularly in the development of new analgesic drugs.

Pharmacological evaluation of the anti-inflammatory activity of a citrus bioflavonoid, hesperidin, and the isoflavonoids, duartin and claussequinone, in rats and mice

Pretreatment of rats with hesperidin (50 and 100 mg kg-1, s.c.) reduced the paw oedema induced by carrageenan by 47 and 63%, respectively, within 5 h. The effect was equivalent to that produced by indomethacin (10 mg kg-1, p.o.), although unrelated to the administered dose, particularly at high doses. At 100 mg kg-1 hesperidin decreased the rat paw oedema induced by dextran by 33%, without influencing the histamine-induced paw oedema. Hesperidin also inhibited pleurisy induced by carrageenan, reducing the volume of exudate and the number of migrating leucocytes by 48 and 34%, respectively, of control values. Equal doses of duartin and claussequinone were ineffective in all the above tests. Pretreatment of mice with hesperidin (100 mg kg-1, s.c.) reduced acetic acid-induced abdominal constriction by 50%, but did not affect the tail flick response. Hyperthermia induced by yeast in rats was slightly reduced by hesperidin. No lesions of the gastric mucosae were detected in rats pretreated with hesperidin. The results indicate that hesperidin obtained from citrus cultures may present a potential therapeutical use as a mild anti-inflammatory agent, being also useful as a precursor of new flavonoids endowed with such activity.

Inhibition of intestinal motility and secretion by flavonoids in mice and rats: structure-activity relationships

Intraperitoneal administration of some flavonoids (apigenin, flavone, kaempferol, morin, myricetin, naringin and rutin; 12.5-50 mg kg-1) significantly (P < 0.05-0.01) reduced small (28-69%) and large (83-134%) intestinal transit in mice. Other flavonoids (naringenin, silibinin, silymarin and taxifolin, 100-200 mg kg-1) reduced (23-41%; P < 0.05-0.01) intestinal transit at doses of 100-200 mg kg-1 while hesperitin, catechin and phloridzin (up to 200 mg kg-1) had no effect. This effect was antagonized by yohimbine (87-96%) and phentolamine (87-91%) but not by prazosin, propranolol, atropine, hexamethonium, mepyramine, cyproheptadine and naloxone. Yohimbine (92-96%) also antagonized the inhibitory effect of flavonols (12.5-50 mg kg-1) (P < 0.05-0.01) on intraluminal accumulation of fluid and diarrhoea induced by castor oil. By contrast, verapamil potentiated the flavonol effect. It is suggested that these effects, influenced by the structure of the molecules, are mediated by alpha 2-adrenergic receptors and calcium.

A study on the role of cholinergic and gamma amino butyric acid systems in the anti-nociceptive effect of gossypin

1. The participation of cholinergic and gamma amino butyric acid (GABA) neurotransmitter systems in the anti-nociceptive effect of gossypin was investigated using pharmacological tools. 2. Physostigmine potentiated its anti-nociceptive response while atropine failed to modify it significantly. 3. THIP (4,5,6,7-tetra hydroisoxazolo (5,4-C) pyridin-3-ol) and gossypin treatment produced an additive response while bicuculline attenuated the anti-nociceptive response of gossypin. Similar observations were recorded for morphine. 4. It is suggested that cholinergic and GABAergic systems play a role in gossypin-induced anti-nociception.

Analgesic activity of certain flavone derivatives: a structure-activity study

1. Flavone, its methoxy derivatives and flavanone were synthesized by standard methods and were tested for analgesic activity in mice by employing acetic acid writhing and tail flick methods. 2. All the tested compounds except flavanone exhibited significant dose-dependent analgesic activity in both the assay models. Some of the compounds were found to involve opioid mechanisms in their analgesic effect. 3. A definite structure-activity relationship was observed in the analgesic activity of flavone derivatives as well as in their mechanism of action.

Dermal intoxication of mice with bis(2-chloroethyl)sulphide and the protective effect of flavonoids

The influence of dermal application of sulphur mustard (SM) on hepatic lipid peroxidation and the protective effect of flavonoids in SM toxicity was investigated. SM applied on the skin of mice (0.25 or 0.5 LD50) depleted glutathione (GSH) in blood and liver. Malondialdehyde (MDA) levels in the liver showed an increase indicating lipid peroxidation. Administration of vitamin E or two flavonoids, gossypin (GN) and hydroxyethyl rutosides (HR) after dermal application of SM did not alter depletion of GSH but did reduce the MDA level significantly. Survival time of mice with 1 LD50 SM applied dermally was increased by GN and HR to a greater extent than by vitamin E or sodium thiosulphate probably due to one or more of the analgesic, anti-inflammatory, antihepatotoxic, antihistaminic, mast cell stabilization, lipid peroxidation inhibitory and free radical scavenging actions of the flavonoids. The present study indicates that dermally applied SM can induce lipid peroxidation and GSH depletion, and flavonoids may be beneficial in reducing the toxicity.

Involvement of calcium in flavonoid analgesia

Calcium has been reported to play a key role in opioid analgesia. Several flavonoids also elicit an analgesic effect through the opioid system. The involvement of calcium in the analgesic activity of these flavonoid compounds was now investigated. Calcium antagonised the analgesic action of flavonoids while nifedipine, a calcium channel blocker, potentiated it. This suggests a possible role for calcium in the analgesic action of flavonoids as with that of morphine.