The Antidepressant Mechanism Of Ammoxetine

Depression is an emotional and mental disorder which is due to CNS biochemical dysregulation and characterized by obvious and long-time low mood. It is the most common mental disorder and also the most important cause of disability. Almost 430 million people are suffering from depression worldwide. WHO has estimated that depression will be one of the second severe disease, right behind ischemic heart disease. The biochemical changes of depression are complicated and the mechanism of depression is still unclear. The most classical hypothesis proposed by the researchers is the monoamine hypothesis which claimed that low levels of monoamines, especially serotonin(5-HT) and norepinephrine(NE), play a key role in the occurrence of depression. This hypothesis has successfully guided the research and development of most first-line antidepressants although it cannot explain the problem of their long therapeutic delays. Recently increasing attention has been paid to the relationship between cytokine and depression. The cytokine hypothesis mentioned that depression is a mental-neural-immune dysfunction. Neuroimmune and neuroendocrine may play an important role in the etiology of depression.Among lots of therapeutic methods, pharmacotherapy is the most important and commonenst way. The clinical commonly used antidepressants are often divided into tetracyclic antidepressants, monoamine oxidase inhibitor, selective serotonin reuptake inhibitor, selective norepinephrine reuptake inhibitor and serotonin-norepinephrine reuptake inhibitor, et al. according to their effect and chemical structure. It has been reported that SNRI acted more effectively and efficiently than SSRI, and had fewer side effects than TCA. In addition, SNRI can effectively relieve many somatic symptoms of depression. Therefore, SNRI has become the first-line antidepressants. To design and synthesis new type of antidepressant has been the key and hot point of neuropsychiatry drugs research and development. Our previous study took duloxetine as the leading compound and synthesized lots of compounds with novel structures. After screening we found that((±)-3-(benzo[d] [1, 3] dioxol-4-yloxy)-N-methyl-3-(thiophen-2-yl) propan-1-amine) showed robust antidepressant activity and had low hepatotoxicity and neurotoxicity compared with duloxetine. The present study has designed to make further explorations of the antidepressant mechanism on ammoxetine arrounding monoamine hypothesis and cytokine hypothesis.Firstly, we use pharmacological models, monoamine depletion models and microdialysis technique in free-moving animals to study the possible antidepressant mechanism of ammoxetine centre on monoamine hypothesis. In pharmacological models, 5-HTP induced mice head twitches and high dose of apomorphine induced hypothermia test were performed to evaluate the effect of ammoxetine on monoaminergic nerve. Acute administration of ammoxetine at dose of(10,20 mg·kg-1) or(2.5、5、10、20 mg·kg-1) could significantly increase the time of head twitches or reverse hypothermia induced by high dose of apomorphine compared with normal control group, indicating that ammoxetine could enhance the function of serotoninergic and norepinephrine nerve. In monoamine depletion models, PCPA/PCA or AMPT were used to deplete the serotonin or norepinephrine in mice brain. Treatment of mice with PCPA or AMPT produced significant increase in the duration of immobility in the tail suspension test. Ammoxetine at dose of 20 mg·kg-1 could significantly reduce the immobility time and increase the concentration of serotonin or norepinephrine in PCA deplete serotonin mice or AMPT deplete norepinephrine mice. Later we used the microdialysis technique in free-moving animals and HPLC-ECD technique to investigate the effect of ammoxetine on the extracellular level of monoamine neurotransmitters in hippocampus. The results indicated that treatment with ammoxetine(10 and 20 mg·kg-1) significantly increased the concentration of 5-HT and NE, with no influence on DA.On the other hand, we used LPS-induced immune response, reserpine-induced depression model and learned helplessness model in mice to investigate the possible mechanism based on cytokine hypothesis. In LPS-induced depression model, treatment with LPS significantly decreased the immobility time in tail suspension test and forced swimming test and ammoxetine improved the depressive-like behavior. Then we used duloxetine, reboxetine and fluoxetine as positive control drugs in TST and FST and sucrose water preference test, the results indicated that LPS could increase the immobility time in TST and FST, and also reduce the preference of sucrose water, ammoxetine and other antidepressants showed antidepression effect in these tests. Then the method of ELISA and HPLC-ECD were used to measure the pro-inflammatory cytokine level and the concentration of 5-HT and NE in mice brain. The results indicated that LPS significantly increased the pro-inflammatory cytokine(IL-1β, IL-6 and TNF-α) level and decreased the concentration of 5-HT and NE in mice brain, which could be reversed by ammoxetine AMX of 10 mg·kg-1.Then, we employed learned helplessness model in mice to evaluate the influence of ammoxetine on the level of cytokine in mice brain tissue. After one week electric shock, the pro-inflammatory cytokine(IL-1β, IL-6 and TNF-α) level of model group significantly increased compared with normal control group, and AMX 10 mg·kg-1 improved the pro-inflammatory cytokine(IL-1β, IL-6 and TNF-α) level to normal. At last, we used another classical depression model to study the effect of ammoxetine on the concentration of cytokine in mice brain. In reserpine-induced depression model test, after being pretreated with reserpine for one week, the pro-inflammatory cytokine(IL-1β, IL-6 and TNF-α) concentration of model group were higher than control group. Treatment with ammoxetine reversed the high level of pro-inflammatory cytokine.In conclusion, the antidepression effect of ammoxetine is closely related to the enhancement of serotoninergic and norepinephrine neurotransmission and regulation of neuro-immune function.