Brain levels of tofizopam in the rat and relationship with benzodiazepine receptors

A Comparison of the Anxiolytic Properties of Tofisopam and Diazepam: A Double-Blind, Randomized, Crossover, Placebo-Controlled Pilot Study

New clinical reports have recently been published on tofisopam-an anxiolytic drug currently registered as a benzodiazepine-after a long break in this research area. Neurobiological studies concerning its properties, which differ from those of benzodiazepines, are underway. The analyses presented in this study aimed to compare the effects of tofisopam, diazepam, and a placebo in the treatment of anxiety symptoms. A total of 66 outpatients (43 women and 23 men) with generalized anxiety disorder aged 19 to 74 years (M = 41.4; SD = 13.2) were randomized in three groups receiving (1) tofisopam (50 mg three times a day), (2) diazepam (5 mg three times a day), or (3) a placebo for 2 weeks. Then, throughout a 2-week washout period, the patients were monitored for withdrawal symptoms. During the last 2 weeks, the effects of tofisopam (50 mg three times a day) and diazepam (5 mg three times a day) were compared (crossover design). The mean improvement on the Hamilton Anxiety Rating Scale was significantly higher in both the tofisopam and diazepam groups compared to the placebo group. There were no significant differences between the effects of diazepam and tofisopam, whereas adverse effects and withdrawal symptoms occurred less frequently in the tofisopam group. Tofisopam did not impair cognitive abilities, and related withdrawal symptoms resembled those of the placebo. If larger future studies corroborate these findings, tofisopam should be classified as a homophtalazine.

Anxiolytic 2,3-benzodiazepines, their specific binding to the basal ganglia

Over the past 20 years, several members of the 2,3-benzodiazepine family have been synthesized. Some of these compounds--tofisopam (Grandaxin), girisopam, nerisopam--exert significant anxiolytic and antipsychotic activities. Sites where actions of 2,3-benzodiazepines are mediated differ from those of 1,4-benzodiazepines. Binding of 2,3-benzodiazepines to neuronal cells in the central nervous system shows a unique and specific distribution pattern: their binding sites are located exclusively to the basal ganglia. Chemical lesioning of the striato-pallido-nigral system, surgical transections of the striato nigral pathway and the activation of c-fos expression in the basal ganglia after application of 2,3-benzodiazepines suggest that these compounds mainly bind to projecting neurons of the striatum. The binding sites are transported from the striatum to the substantia nigra and the entopeduncular nucleus. Recent studies on mechanism of action of 2,3-benzodiazepines indicate their possible role in opioid signal transduction since 2,3-benzodiazepines augment the agonist potency of morphine to induce catalepsy and analgesia, and their action is diminished in morphine tolerant animals. The possible biochemical target of 2,3-benzodiazepines is an alteration in the phosphorylation of protein(s) important in the signal transduction process. Agents affecting emotional responses evoked by endogenous opioids without danger of tolerance and dependence may represent a new therapeutic tool in the treatment of addiction and affective disorders.

Is tofisopam an atypical anxiolytic?

This review describes the behavioural and biochemical profile of tofisopam, a 3,4-benzodiazepine that differs considerably in its effects and mechanisms of action from classical 1,4-benzodiazepines. In man tofisopam appears to possess anxiolytic activity without appreciable sedative and muscle relaxant side effects; in animals, however, tofisopam totally lacks anxiolytic and anticonvulsant properties in tests sensitive to the effects of 1,4-benzodiazepines. Tofisopam also has mixed dopamine agonist and antagonist-like properties in several in vivo and in vitro tests in animals. The possible relevance of the latter effects to the unusual behavioural profile of tofisopam are discussed, and its effects compared with those of buspirone, a novel anxiolytic that has similar activity at benzodiazepine and dopamine systems. It is proposed that these two drugs may represent a novel class of compounds that reduce anxiety by increasing the ability of patients to cope with daily tasks, rather than classical anxiolytics, that reduce anxiety by tranquilization.

Affinity of various compounds for benzodiazepine binding sites in rat brain, heart and kidneys in vitro

Binding of several psychoactive, antiinflammatory, antihypertensive, and antiarrhythmic drugs to central and peripheral benzodiazepine (BZ) binding sites was studied in the brain, heart and kidneys of rats. Diazepam exhibited the highest affinity for all binding sites (Ki values at 0.01 microM level); another 1,4-BZ, oxazepam, had markedly lower affinity for peripheral binding sites (Ki 21-37 microM). Non-BZ compounds had low affinity for central BZ receptors; proquazone was the most potent (Ki 9.5 microM). The affinities of non-BZ compounds were higher for peripheral BZ binding sites. The Ki value for proquazone was approximately 0.1 microM; and many other antiinflammatory agents, and the vasodilators cyclandelate and nifedipine, produced Ki values in the micromolar level. beta-Blocking drugs, and several other antihypertensive and antiarrhythmic agents lacked affinity for both central and peripheral BZ binding sites. According to the results, the affinity for peripheral binding sites is independent of an affinity for central BZ receptors. Non-BZ compounds that bound to brain BZ receptors bound with equal affinity to both BZ1 and BZ2 subgroups of receptors. The compounds with affinity for peripheral BZ binding sites did not select between heart and kidneys, which suggests that these organs have similar binding sites. The role of the peripheral BZ binding sites has not yet been established. The findings of this study allow the selection of a more varied group of ligands to be used when investigating the physiological significance of these binding sites.

Effects of diazepam, tofizopam or phenytoin during foetal development on subsequent behaviour and benzodiazepine receptor characteristics in rats

The development of rats was studied for 3 postnatal weeks after prenatal medication with diazepam (10 mg/kg/day), phenytoin (50 mg/kg/day), or tofizopam (50 mg/kg twice daily) given by gastric intubation from day 7 to 21 of pregnancy. The treatments had no effect on the litter size. There were also no differences between the groups in a battery of tests for development (negative geotaxis, righting reflex, cliff avoidance, rotarod, passive avoidance), but the activity spurt seen at postnatal days 18-21 was missing in pups of diazepam-treated mothers. The number of benzodiazepine receptors and their affinity for tritiated flunitrazepam developed similarly in all of the rat groups. Thus, the transient changes in motor development seen 2-3 weeks after birth of rats whose mothers received diazepam during pregnancy do not seem to be related to changes in ontogenesis of benzodiazepine receptors.

Indirect dopaminergic effects of tofisopam, a 2,3-benzodiazepine, and their inhibition by lithium

Tofisopam, a 2,3-benzodiazepine, has been shown to have anxiolytic activity. However, in contrast to the widely used 1,4-benzodiazepines, it has no anticonvulsant, sedative or muscle relaxant effects. Tofisopam enhanced the behavioural actions of various dopaminergic drugs, both direct agonists, such as apomorphine (climbing behaviour in mice), and indirect agonists, such as (+)-amphetamine and amineptine (jumping behaviour in mice). Chronic treatment with lithium abolished the tofisopam-induced increase in the activity of these dopaminergic drugs. Thus tofisopam appears to induce acutely an increase in the sensitivity of central dopaminergic receptors which can be prevented by pretreatment with lithium.

Effects of denzimol on benzodiazepine receptors in the CNS: relationship between the enhancement of diazepam activity and benzodiazepine binding sites induced by denzimol in the rat

Denzimol, a new anticonvulsant drug with a pharmacological profile similar to that of phenytoin, enhances the ataxic and antimetrazol activity of diazepam in rats without affecting its activity against picrotoxin-induced seizures. In vivo and ex vivo denzimol enhances the binding of 3H-flunitrazepam in cortex and in hippocampus but not in cerebellum. The possibility of this increase in the number of benzodiazepine binding sites contributing in some way to enhancement of the depressive and anticonvulsant activity of diazepam is discussed.

Increased number of brain benzodiazepine receptors after in-vivo administration of estazolam to rats

Estazolam significantly increased the Kd of [3H]flunitrazepam in-vitro, like other benzodiazepines (BDZs) acting competitively at the receptor site. At variance with other BDZs, estazolam significantly raised the Bmax for [3H]flunitrazepam, at concentrations lower than its Ki for BDZ receptors. This effect may be responsible for the observed increase in [3H]diazepam binding after in-vivo administration of estazolam to rats.