Beatrice Guardiola-Lemaitre

Agomelatine, the first melatonergic antidepressant: discovery, characterization and development

Current management of major depression, a common and debilitating disorder with a high social and personal cost, is far from satisfactory. All available antidepressants act through monoaminergic mechanisms, so there is considerable interest in novel non-monoaminergic approaches for potentially improved treatment. One such strategy involves targeting melatonergic receptors, as melatonin has a key role in synchronizing circadian rhythms, which are known to be perturbed in depressed states. This article describes the discovery and development of agomelatine, which possesses both melatonergic agonist and complementary 5-hydroxytryptamine 2C (5-HT2C) antagonist properties. Following comprehensive pharmacological evaluation and extensive clinical trials, agomelatine (Valdoxan/Thymanax; Servier) was granted marketing authorization in 2009 for the treatment of major depression in Europe, thereby becoming the first approved antidepressant to incorporate a non-monoaminergic mechanism of action.

Successful use of S20098 and melatonin in an animal model of delayed sleep-phase syndrome (DSPS)

In human delayed sleep-phase syndrome (DSPS), sleep onset and wake times occur far later than normal. In the population, DSPS may be an important contributor to complaints of sleep onset insomnia. We previously reported an animal model of DSPS in laboratory rats in which the onset of nocturnal activity is delayed by several hours [negative phase angle difference (PAD)]. The effect of melatonin 1 mg/kg SC and S20098 (Servier) 1 and 3 mg/kg on the negative PAD was investigated over 22 days of injections. In comparison to control injections of dimethylsulfoxide (DMSO), both melatonin and S20098 over approximately 9 days phase advanced the onset of activity toward the onset of darkness. At cessation of injections, activity onset delayed over approximately 11 days back toward, but as a group did not reach the original PAD. This effect of melatonin on the phase angle of entrained rats is consistent with its effects on delayed sleep in humans. It is likely, therefore, that S20098 may be of use to ameliorate DSPS in humans.

Melatonin analogues as agonists and antagonists in the circadian system and other brain areas

We studied the effects of drugs related to melatonin on neuronal firing activity in the suprachiasmatic nucleus, intergeniculate leaflet and other brain areas in urethane-anesthetized Syrian hamsters. We tested melatonin and two naphthalenic derivatives of melatonin, a putative agonist (S20098: N-[2-(7-methoxy-1-naphthyl)ethyl]acetamide), and a putative antagonist (S20928: N-[2-(1-naphthyl)ethyl]cyclobutyl carboxamide). Both melatonin and S20098 given intraperitoneally (i.p.) were able to suppress firing rates of cells in a similar dose-dependent manner, but the effects of S20098 were longer lasting. Iontophoresis of melatonin dose dependently depressed spontaneous and light-evoked activity of cells in the suprachiasmatic nucleus and intergeniculate leaflet, while iontophoresis of S20098 was relatively ineffective, probably because it is a poorly charged compound. S20928 (2.0-10 mg/kg, i.p.) alone decreased firing rates of light-sensitive cells by 25-50% for 5-30 min in the suprachiasmatic nucleus and intergeniculate leaflet; however, low doses (< 2.0 mg/kg) of S20928 partially blocked the effects of melatonin agonists on most cells. The non-selective serotonin antagonist metergoline did not block the effects of either melatonin agonist. Both melatonin agonists and antagonists were less effective when applied to cells in the hippocampus and dorsal lateral geniculate nucleus. These results indicate that S20098 is an agonist acting probably on melatonin receptors in the Syrian hamster brain. S20928 may have mixed agonist/antagonist properties, but at low doses appears to function as an antagonist at melatonin receptors in the suprachiasmatic nucleus and intergeniculate leaflet.

Entrainment of circadian rhythms by S-20098, a melatonin agonist, is dose and plasma concentration dependent

The present study determined first the dose-response (0.5 to 10 mg.kg-1) to daily oral administration of S-20098, a melatonin agonist, in entraining circadian rhythms of rats free-running in constant darkness; second, the relation between entrainment and the plasma concentration of S-20098. Finally, responses to 8 mg.kg-1 of S-20098 were compared with those obtained with the same dose of melatonin and ipsapirone. Responses were classified as negative, transient, or true entrainment. The data indicated a clear dose-dependent response from 2.5 to 10 mg.kg-1 of S-20098 with an ED50 of 5.7 mg.kg-1 for true entrainment and a clear relation between entrainment and the plasma concentration of S-20098. S-20098 was as effective as melatonin to entrain free-running rhythms. Ipsapirone was ineffective in our experimental conditions.

Combined effects of diazepam and melatonin in two tests for anxiolytic activity in the mouse.

The effects of behaviorally nonactive doses of melatonin and diazepam were investigated in two test models for anxiolytics in mice to see whether mutual enhancement could be observed when the two treatments were combined. The test models used were the four plates test and the tail suspension test. In the former test anxiolytics increase the number of punished crossings and in the latter increase the duration of immobility of mice suspended by the tail. In the four plates test combined treatment with melatonin (128 and 256 mg/kg IP) and diazepam (0.5 mg/kg PO) caused a significant increase in the number of punished crossings, whereas each treatment alone was without effect. Similarly, in the tail suspension test, a clear increase in the duration of immobility was observed after combined treatment (256 mg/kg IP melatonin + 0.5 mg/kg PO diazepam), whereas no effects were observed with the individual treatments alone. These results suggest that melatonin can enhance the anxiolytic actions of diazepam.

Agomelatine: mechanism of action and pharmacological profile in relation to antidepressant properties

Agomelatine behaves both as a potent agonist at melatonin MT1 and MT2 receptors and as a neutral antagonist at 5‐HT2C receptors. Accumulating evidence in a broad range of experimental procedures supports the notion that the psychotropic effects of agomelatine are due to the synergy between its melatonergic and 5‐hydroxytryptaminergic effects. The recent demonstration of the existence of heteromeric complexes of MT1 and MT2 with 5‐HT2C receptors at the cellular level may explain how these two properties of agomelatine translate into a synergistic action that, for example, leads to increases in hippocampal proliferation, maturation and survival through modulation of multiple cellular pathways (increase in trophic factors, synaptic remodelling, glutamate signalling) and key targets (early genes, kinases). The present review focuses on the pharmacological properties of this novel antidepressant. Its mechanism of action, strikingly different from that of conventional classes of antidepressants, opens perspectives towards a better understanding of the physiopathological bases underlying depression.

Interindividual differences in the pattern of melatonin secretion of the Wistar rat.

Abstract: In vivo trans‐pineal microdialysis was performed in male Wistar rats maintained under a 12 hr light: 12 hr dark (LD 12: 12) cycle. Collected dialysates were assayed by radioimmunoassay for melatonin concentrations. A non‐linear regression was fitted through the obtained datapoints to determine the time points at which a 50% increase (IT50) and decrease (DT50) of the nocturnal melatonin peak were reached. In a first experiment, the nocturnal melatonin profiles of four animals were determined throughout 5 consecutive days. In a second experiment, we analysed the melatonin profiles during the night in rats originating from three different breeding colonies (Dépré, Harlan, and Iffa‐Crédo). A low intraindividual variability was found on the phase markers IT50 and DT50, as on peak duration of melatonin rhythms estimated over 5 subsequent days in the same animal. In contrast, animals showed a large interindividual variability in their profile phase markers and the values were dependent on the origin of the breeding colony. Each rat colony was characterized by early or late IT50 and DT50 as long or short peak length. It is concluded from experiment 1 that the melatonin rhythm is a very stable circadian marker. Nevertheless, great caution must be taken in the choice of animal groups while studying circadian rhythms due to the large interindividual variability observed in experiment 2. Therefore, as the technique allows the use of the animal as its own control, the present study demonstrated that the use of the microdialysis technique is of interest in studies on the circadian system.

Melatonin receptors mediate contraction of a rat cerebral artery

MELATONIN receptors are expressed in the cerebral arteries of the rat which form the circle of Willis. We report here that melatonin induces contraction of in vitro preparations of pressurized rat posterior communicating artery, in a concentration-dependent manner. This action of melatonin is inhibited by S-20928, a specific melatonin receptor antagonist. Our results demonstrate that the contractile action of melatonin is mediated by its receptors in the cerebral artery, and suggest a role for melatonin in the regulation of cerebral circulation.

Effects of a Daylight Cycle Reversal on Locomotor Activity in Several Inbred Strains of Mice

There is some evidence of melatonin implication in the nycthemeral regulation of running activity rhythm in rodents. Because some inbred strains of mice such as C57BL/6 and BALB/c have been generally found to present no nocturnal melatonin peak, in contrast to others such as C3H/He and CBA mice, the aim of this study was to examine the adaptation of daily locomotor activity to a light/dark cycle phase shift in these four strains. An apparatus consisting of two boxes connected by a tunnel was used to record spontaneous locomotor activity, defined as the number of transitions between the two boxes. Locomotor activity was monitored continuously during 3 days before and 14 days after a 12-h phase delay of the light/dark cycle. Results essentially showed that the adaptation of the locomotor activity rhythm to the phase shift was faster in C57BL/6 and BALB/c mice than in C3H/He and CBA mice. This could be related, at least in part, to the differences in melatonin synthesis between the former strains and the latter ones. Although melatonin nocturnal peak is not necessary to a daylight regulation of circadian functions in rodents, it could be considered as an endocrine message that takes part in the anticipation of the following light/dark cycle.

Potent antihyperglycaemic property of a new imidazoline derivative S-22068 (PMS 847) in a rat model of NIDDM

Recent data suggest that some imidazoline derivatives can lower plasma glucose in experimental animal models of diabetes. We studied the activity of an imidazoline S‐22068, in rat model of non‐insulin‐dependent diabetes mellitus (NIDDM) produced with a low dose of streptozotocin (35 mg kg−1, i.v.) in the adult. The respective increase over basal value in glucose (ΔG) and insulin (ΔI), and the rate of glucose disappearance (K), were measured during a 30 min intravenous glucose tolerance test. After an intraperitoneal injection of S‐22068 (24 mg kg−1), ΔG (mM min −1) was decreased (91.67±5.83 vs 120.5±3.65; P<0.001), whereas K was increased (1.74±0.09 vs 1.18±0.05; P<0.001). Although insulinaemia was increased at time‐point 0 of the test, ΔI was unchanged. During oral glucose tolerance tests (OGTT), S‐22068 (24 mg kg−1, p.o.) improved glucose tolerance, and its efficiency was potentiated after chronic treatment (15 days). Basal glycaemia was unaffected by the treatment. Under the same conditions, a higher dose of S‐22068 (40 mg kg−1) further improved glucose tolerance without causing hypoglycaemia. Binding experiments revealed that S‐22068 displays no affinity for either adrenoceptors or the two imidazoline receptors I1 or I2. These results demonstrate that S‐22068 improves glucose tolerance without causing hypoglycaemia. Thus S‐22068 represents a new potential option in the treatment of NIDDM.