Role Of Endocannabinoid System In Depression Induced By Tumor-bearing Stress

Depression is the most prevalent psychiatric disorder in advanced cancer patients. Antidepressant treatment is the important component of the combined treatment in cancer patients aiming to improve the quality of life. Having an essential role in the regulation of stress reaction and emotion, Endocannabinoid system is closely related to the pathogenesis of depression. The endogenous ligands of cannabinoid receptors, anadamide and 2-arachdonyl glycerol are synthesized and secreted under the modulation of neuronal impulse, consequently, activate the endocannabinoid signaling and then modulate the neuroplasticity and maintain the neuronal homeostasis. Our previous studies have shown that tumor-bearing state could induce the depressive behavior change in mice, as well as the specific gene expression and metabolites change in brain. In order to explore the biological mechanism of depression induced by tumor-bearing state, the alteration of endocannabinoid system was measured in tumor-bearing mice.This study included: 1. A surrogate analyte-based LC-MS/MS method was developed and validated to assess the concentrations of endocannabinoids in peripheral plasma and prefrontal cortex,hippocampus,hypothalamus. The calibration curves were constructed with use of stable isotope-labeled AEA-d4 and 2-AG-d5 in true biological matrices to determine AEA and 2-AG, the linear range of which were 0.325~32.5 ng/mL and 11~5500 ng/m L respectively. 2. The expression of CB1 and FAAH in brain substructures were analyzed with Western blot technology. 3. The level of corticosterone was studied with a commercial EIA kit. The effect of different antidepressants and FAAH inhibitor URB597 and CB1 agonist Win55,212-2 were used separately to observe their effect on the level of corticosterone in tumor-bearing mice.A sensitive and reliable LC–MS/MS method for simultaneous determination of AEA and 2-AG in murine plasma and brain tissues was established. This assay employed a "surrogate analyte" approach which eliminated the interference from the endogenous analytes. The result showed that the concentration of AEA in three different brain substructures decreased in tumor-bearing mice compared with the control group, with no change of 2-AG concentration in hippocampus and hypothalamus.The plasmic concentration of endocannabinoids remained unchanged. The expression of CB1 receptor and FAAH were found to be higher in the hippocampus of tumor-bearing mice than of control group. The concentration of plasma coticosterone increased in tumor-bearing mice compared with control group. A fortnight treatment of fluoxetine and agomelatine significantly reversed the increased levels of plasma corticosterone induced by tumor-burden state. Treatment with FAAH inhibitor URB597 also decreased the enhanced level of plasma corticosterone as well as of brain corticosterone in the tumor-bearing mice. Treatment with CB1 agonist Win55,212-2 was invalid to decrease the high level of corticosterone in tumor-bearing mice.In summary, the tumor-bearing state could induce the alteration and dysfunction of endocannabinoid system both in brain and in plasma, which might play crucial role in the stress reaction and the pathogenesis of depression. The inhibition of degradation of AEA could exert potent ameliorating effect on the depression induced by tumor-bearing state.