Возможные механизмы антидепрессивного действия антипсихотиков второго поколения

Although the exact mechanism of SGAs for MDD has not yet been clearly elucidated, several plausible underlying mechanisms are listed as follows: modulation of crucial neurotransmitter receptors and transporters such as dopamine, serotonin and noreinephrine resulting in net effect of enhancement of such neurotransmitters' transmission, effects on sleep, alteration of various hormones (ACTH, sex hormones, etc.), modification of immune functions including modulation of inflammation process (cytokines, etc.), antioxidation process and modulation of neurotrophic factors (BDNF, etc).[13]

Specifically, the main pharmacological rationale of SGAs as an antidepressant augmentation would be based on their effects on monoamine transporters or receptors of crucial neurotransmitters such as serotonin, norepinephrine and dopamine, which are also the main target of contemporary antidepressants. The partial agonism at D2 and/or D3 receptors may increase dopamine neurotransmission at the prefrontal cortex. The increase in the dopamine concentration in the prefrontal cortex may be also indirectly related to the antidepressive effect of 5-HT1A receptor agonist.[14,15] The antidepressant effect may also be mediated by 5-HT1A partial agonism and/or antagonism at 5-HT2A receptors.[16–18] Although, still controversial, the antidepressant effect of 5-HT1A receptor agonists may be predominantly mediated by postsynaptic 5-HT1A receptors, while the anxiolytic effect would be mainly associated with presynptic 5-HT1A receptors.[19] The antagonism of the 5-HT2C receptors has been also found to be involved in increased dopamine and norepinephrine transmission.[20] It is also well known that high affinity at the α2-adrenergic receptor may enhance the release of norepinephrine.[21] Unlike any other SGAs, ziprasidone was reported to block synaptic serotonin, norepinephrine and dopamine reuptake in vitro.[22,23] Evidence indicates that both 5-HT6 agonists and antagonists may evoke identical responses in animal models of MDD, although the possible mechanisms of these effects seem to be diverse and are not clearly understood. The augmented effects were notable by combining antidepressants with a selective 5-HT6 receptor antagonist.[24] There is also a considerable amount of evidence supporting a role for the 5-HT7 receptor in MDD. The blockade of the 5-HT7 receptor led to antidepressant-like effects in animal models of MDD. It should be also worthy to mention that augmentation of 5-HT7 receptor antagonists with antidepressants was remarkable in animal models of MDD.[25]

Another mechanism involving in the action of SGAs should be the alteration of the glutamate receptor activity, and thus restoring normal glutamatergic neurotransmission and reducing the chances of excitotoxicity.[26] Some SGA treatment may also cause a decrease in plasma adrenocorticotropic hormone concentration and a normalization of HPA-axis dynamics.[27] An impaired neuroprotection has also been implicated in the pathophysiology of MDD.[28,29] Interestingly, activation of the 5-HT1A receptors was shown to be neuroprotective against various brain insults such as N-methyl-daspartic acid.[30] Some SGAs have also demonstrated such neuroprotective effects indicating a potential role in the protection against excitotoxicity in vivo.[30]

Overall 5-HT2A antagonism should be a commonly shared biological relevance for most of the SGAs as a potential mechanism of their antidepressant effect. Interactive effects with the dopaminergic system may be more distinct with the action mechanism of amisulpride and aripiprazole, while norepinephrine- and/or serotonin-reuptake inhibition should be the unique case with quetiapine or ziprasidone.[31] Each antipsychotic has a distinct profile of affinities towards different neurotransmitter receptors, which should be associated mainly with mediation of antidepressant-like effects.

Second-generation Antipsychotics in the Treatment of Major Depressive Disorder

эндокринные эффекты нормотимиков

Both seizures and antiepileptic drugs may induce disturbances in hormonal system. Regarding endocrine effects of anticonvulsants, an interaction of these drugs with gonadal, thyroid, and adrenal axis deserves attention. Since majority of antiepileptic drugs block voltage dependent sodium and calcium channels, enhance GABAergic transmission and/or antagonize glutamate receptors, one may expect that similar neurochemical mechanisms are engaged in the interaction of these drugs with synthesis of hypothalamic neurohormones such as gonadotropin-releasing hormone (GnRH), thyrotropin-releasing hormone (TRH), corticotropin-releasing hormone (CRH) and growth hormone releasing hormone (GHRH). Moreover some antiepileptic drugs may affect hormone metabolism via inhibiting or stimulating cytochrome P-450 iso-enzymes. An influence of antiepileptic drugs on hypothalamic-pituitary-gonadal axis appears to be sex-dependent. In males, valproate decreased follicle-stimulating hormone (FSH) and luteinizing hormone (LH) but elevated dehydroepiandrosterone sulfate (DHEAS) concentrations. Carbamazepine decreased testosterone/sex-hormone binding globulin (SHBG) ratio, whereas its active metabolite--oxcarbazepine--had no effect on androgens. In females, valproate decreased FSH-stimulated estradiol release and enhanced testosterone level. On the other hand, carbamazepine decreased testosterone level but enhanced SHBG concentration. It has been reported that carbamazepine, oxcarbazepine or joined administration of carbamazepine and valproate decrease thyroxine (T4) level in patients with no effect on thyrotropin (TSH). While valproate itself has no effect on T4, phenytoin, phenobarbital and primidone, as metabolic enzyme inducers, can decrease the level of free and bound thyroxine. On the other hand, new antiepileptics such as levetiracetam, tiagabine, vigabatrine or lamotrigine had no effect on thyroid hormones. With respect to hormonal regulation of metabolic processes, valproate was reported to enhance leptin and insulin blood level and increased body weight, whereas topiramate showed an opposite effect. In contrast to thyroid and gonadal hormones, only a few data concern antiepileptic drug action in HPA axis. To this end, no effect of antiepileptic drugs on adrenocorticotropic hormone (ACTH)/cortisol circadian rhytmicity was found. Valproate decreased CRH release in rats, whereas lamotrigine stabilized ACTH/cortisol secretion. Moreover, felbamate was found to inhibit stress-induced corticosterone release in mice. Interestingly, recent data suggest that felbamat and some other new antiepileptic drugs may inhibit transcriptional activity of glucocorticoid receptors. Summing up, the above data suggest that traditional antiepileptic drugs may cause endocrine disturbances, especially in gonadal hormones.
Endocrine effects of antiepileptic drugs

+ Effects of antiepileptic drugs on immune system

Кортиколиберин-дексаметазоновый тест

Кортиколиберин-дексаметазоновый тест имеет большую специфичность в отношении депрессивных больных по сравнению с дексаметазоновым тестом. Если специфичность дексаметазонового теста не превышала 50%, то, по данным зарубежных авторов, специфичность кортиколиберин-дексаметазонового теста составляет 80-90% (11).

Тест состоит в том, что вечером больной получает дексаметазон - синтетический глюкокортикоид, по принципу обратной связи тормозящий активность гипоталамо-гипофизарно-надпочечниковой оси. На следующий день в 15.00 больному внутривенно вводят кортиколиберин, стимулирующий выброс АКТГ. В норме уровень кортизола и АКТГ остаётся очень низким, т.к. после подавления дексаметазоном ГГН-ось какое-то время не реагирует на стимуляцию. У пациентов с депрессией уровень кортизола и АКТГ резко возрастает через час после введения кортиколиберина, то есть подавление дексаметазоном оказывается недостаточным. Это отмечается в 90% случаев, что делает этот тест достаточно убедительным.
Я.А.Кочетков. - Депрессия и гипоталамо-гипофизарно-надпочечниковая система: новые стратегии изучения