Progress in Neuro-Psychopharmacology and Biological Psychiatry
Harmine produces antidepressant-like effects via restoration of astrocytic functions
Introduction
Major depression is a common disease affecting numerous persons in the world-wide. At present, nearly all of the clinical antidepressants are developed out of the monoaminergic deficit hypothesis of depression, and these agents have been used as classical antidepressants for a very long time (Lanni et al., 2009, Kern et al., 2012). However, more and more studies and clinical reports show that these antidepressants exhibit numerous limitations (Fava, 2010, Fabbri et al., 2013, Sanchez et al., 2015). For example, the first application of traditional antidepressants is effective only in about one-third of patients, and approximately two-third of patients fail to achieve clinical improvements after trying several times (Schwartz et al., 2016). Thus, it is necessary to develop novel mechanism-based antidepressants in order to improve the present status of drug therapy of depression.
Increasing evidence indicates that astrocytic dysfunction is actively involved in the pathogenesis of depression. Decreased numbers of hippocampal astrocytes have been observed in rodents treated with chronic stresses or maternal deprivation (Ye et al., 2011, Leventopoulos et al., 2007). Post-mortem studies of tissues from depressed patients describe reduced numbers of astrocytes in the brain (Oh et al., 2012, Ménard et al., 2016), and these reductions are supported by the finding that the glial fibrillary acidic protein (GFAP)-expressing cells are reduced by chronic stresses in both prefrontal cortex and hippocampus (Banasr and Duman, 2008, Ardalan et al., 2017). In other studies, researchers show that expressions of glial-specific excitatory amino-acid transporters (EAATs: EAAT1/glutamate/aspartate transporter (GLAST), EAAT2/glutamate transporter-1 (GLT-1)) and glutamine synthetase (GS) can be altered in brain tissues from depressed patients (Choudary et al., 2005, Bernard et al., 2011). Functionally, the astrocytic abnormality has been shown to induce a decrease in glutamate uptake and cycling, an accumulation of glutamates, as well as an impairment in brain-derived neurotrophic factor (BDNF) signals and hippocampal neurogenesis (Lutgen et al., 2016, Martin et al., 2012). Thus, inhibition of astrocytic dysfunction may be a potential strategy for depression therapy.
Harmine is a hallucinogenic alkaloid found in the seed of Peganum harmala and Banisteriopsis caapi, both of which are traditionally used for ritual and medicinal preparations in the Middle East, Central Asia, and South America (Sourkes, 1999). In past years, a wide range of pharmacological effects of harmine, such as antioxidation (Moura et al., 2007, Kim et al., 2001), antigenotoxicity (Moura et al., 2007), and anti-diabetes (Waki et al., 2007), have been revealed. Preclinical findings show that harmine has potential antidepressant-like activities in acute and chronic depression models (Fortunato et al., 2009, Fortunato et al., 2010, Aricioglu and Altunbas, 2003, Farzin and Mansouri, 2006). More strong correlations between harmine and depression have been evidenced by recent studies in depressed patients, in which a single dose of ayahuasca, a harmine-containing hallucinogenic plant, has been reported to produce rapid and sustained antidepressant-like activities (Osório Fde et al., 2015, Sanches et al., 2016). Mechanistically, the antidepressant-like effects of harmine may be mediated by restoration of BDNF signals (Fortunato et al., 2009, Fortunato et al., 2010). An inverse-agonistic mechanism located in the benzodiazepine receptors may also mediate the antidepressant-like effects of harmine, as flumazenil, an inhibitor of the benzodiazepine receptor, has been shown to abrogate the antidepressant-like effects of harmine in the forced swimming test (FST) (Aricioglu and Altunbas, 2003). Recently, several different studies show that harmine increases GLT-1 gene and protein expression as well as glutamate uptake activity in animal models of amyotrophic lateral sclerosis (ALS) (Li et al., 2011) and cerebral ischemia (Sun et al., 2014), suggesting that harmine may exert neuroprotective effects via enhancement of GLT-1 functions.
Within these contexts, we hypothesized that harmine exerts antidepressant-like effects likely through restoration of astrocytic functions. As anticipated, we showed that harmine not only prevented mice depressive-like behaviors, but also reversed the reductions in BDNF protein levels and hippocampal neurogenesis induced by CUS. Harmine also prevented CUS-induced decreases in GFAP protein expressions and up-regulated GLT-1 protein expressions in mice hippocampus and prefrontal cortex. Specific inhibition of astrocytic functions abrogated the protective effects of harmine in depressed mice. Since astrocytes contribute critically to the integrity of neuronal functions (Ben Haim and Rowitch, 2017, Yang et al., 2015), our studies indicate that the astrocyte may be a potential target for the antidepressant-like effects of harmine.
Section snippets
Animals
8–10 weeks old male C57BL/6J mice were housed five per cage under standard conditions (12-h light/dark cycle; lights on from 07:00 to 19:00; 23 ± 1 °C ambient temperature; 55 ± 10% relative humidity) for 1 week with free access to food and water. Each experimental group consisted of 10 mice. Behavioral experiments were carried out during the light phase. Animal experiments were conducted in accordance with internationally accepted guidelines for the use of animals in toxicology as adopted by the
Chronic harmine treatment reverses the CUS-induced depressive-like behaviors in C57BL/6J mice
To characterize the antidepressant-like effects of harmine, we employed a widely-used animal model of depression (Jiang et al., 2015b), CUS, in this study. TST and FST have been applied to detect the antidepressant-like activities of potential antidepressants (Steru et al., 1985, Porsolt et al., 1977). In the FST, two-way ANOVA revealed significant effects for stress [F(1, 72) = 39.70, p < 0.001] and drug treatment [F(3, 72) = 7.85, p < 0.001], but not for stress × drug treatment interaction [F(3, 72) =
Discussion
One of the major contributions of this study is the identification of the antidepressant-like effects of harmine, which have been reported in previous studies (Fortunato et al., 2009, Fortunato et al., 2010, Aricioglu and Altunbas, 2003, Farzin and Mansouri, 2006). The major difference between our and other's studies is that we evaluated the antidepressant-like effects of harmine in stressed conditions, while the others did it in normal animals. On the face of it, there seems to be nothing new
Conclusions
Our results are in consistent with a growing number of studies showing that astrocyte dysfunction contributes critically to the development of depression (Ye et al., 2011, Leventopoulos et al., 2007, Oh et al., 2012, Ménard et al., 2016). Harmine, a natural-derived drug reported to increase GLT-1 expression (Li et al., 2011, Sun et al., 2014), reversed the behavioral deficits induced by CUS. The potential involvement of GLT-1 in harmine's effects on depression is supported by previous studies,
Ethical Statements
All animal experiments in this study were conducted in accordance with internationally accepted guidelines for the use of animals in toxicology as adopted by the Society of Toxicology in 1999 and approved by the University Animal Ethics Committee of Nantong University (Permit Number: 2110836).
Acknowledgements
This work was supported by the Natural Science Foundation of China (No. 81571323), the Natural Science Foundation of Jiangsu Province (No. BK20141240), and the Science and Technology Project of Nantong City (No. MS12015050).
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Fengguo Liu and Jingjing Wu contributed equally to this work.