| Background:Diabetes and depression are both serious chronic conditions that negatively affect quality of life,increase functional disability,and reduce life expectancy.Type 2diabetes(T2D),the most common form of diabetes,is characterized by high blood sugar levels due to impaired insulin production in the pancreas and/or insulin resistance in the body’s cells.It accounts for 90 to 95 percent of newly diagnosed cases of adult diabetes,and the risk of developing this type of diabetes increases with age,obesity and physical inactivity.Depression is the most common mental illness,affecting a total of 322 million people worldwide.The nature of depression is that sufferers experience mood swings,loss of interest or pleasure,disturbances in appetite and sleep,and changes in energy levels.It is also accompanied by a decrease in self-care behaviors,such as decreased adherence to medication,poor nutrition and lack of exercise,which are often associated with depression.Previous studies have pointed out that there is a high degree of comorbidity between these two diseases,which has become a hot topic in the field,but the mechanism of comorbidity is still unclear.Activated innate immunity and acute inflammatory response are deeply related to the pathogenesis of T2 D.Specifically,elevated concentrations of proinflammatory factors lead to pancreatic beta cell apoptosis and insulin metabolism disorders that predict T2 D in non-diabetic patients.Similarly,there is growing evidence that pro-inflammatory factor-mediated inflammatory responses are associated with depression in non-diabetic patients.Although there is strong evidence that the innate immune system plays a role in the pathogenesis of depression in the general population,the role of innate immunity in the pathogenesis of depression in patients with T2 D is unclear.The active NLRP3 inflammasome is an important part of innate immunity and inflammatory response,and its production of mature interleukin-1β(IL-1β)and interleukin-18(IL-18)are involved in the pathogenesis of diabetes and depression,respectively.However,its role in the occurrence of comorbidities between type 2diabetes and depression remains unclear.Therefore,the activation of NLRP3 inflammasome and its products may be the common biological origin of NLRP3.Currently,there are quite a few drugs that target to inhibit NLRP3 inflammasome and its products,and their treatment of diabetes and depression has been reported in many literatures.Previous studies have indicated that oridonin is a novel anti-inflammatory plant extract,but its mechanism of action is unclear.Objectives:1.To observe the effects of oridonin on depression-like behavior and glucose metabolism in CUMS rats.2.To observe the efficacy comparison between oridonin and fluoxetine,as well as the effect of their combined use.3.The mechanism of action of oridonin in vivo and in vitro were investigated and verified.Methods:1.Effect of oridonin on depression-like behavior induced by chronic unpredictable stressThe six-week chronic unpredictable stress was used to construct the rat model of depression.Two experimental procedures,prophylactic administration and therapeutic administration,were established according to the time node of the process of depressive behavior in rats.Forced swimming test,sucralose preference test and body weight gain were used to observe the effect of oridonin on depressive behavior,and the efficacy of oridonin and fluoxetine as well as the total effect of combined medication were compared.The activity of microglia cells in the prefrontal cortex and hippocampus of rats was observed by immunofluorescence.2.Effect of oridonin on abnormal glucose metabolism induced by chronic unpredictable stressSix weeks of chronic unpredictability stress was used to construct the model of abnormal metabolism of rats,and the rats were given prophylactic administration of oridonin.The glucose metabolism of rats was observed by glucose tolerance test,insulin tolerance test and glucose stimulated insulin secretion test.Morphological changes of insulin and glucagon and infiltration of macrophages in pancreatic tissues were observed by immunofluorescence.3.The molecular mechanism by which oridonin influences depression-like behavior and insulin resistanceThe activity of NLRP3 inflammasome,namely the expression of IL-1β and IL-18 mature body,in hippocampus and pancreatic tissue was detected by Western blot.In addition,the expression levels of IL-1β,IL-18 and corticosterone in peripheral blood were detected by ELISA assay.Then,the localization of NEK7 and the interaction between NEK7 and NLRP3 were investigated by immunofluorescence and immunoprecipitation.Finally,in vitro cell experiments were used to verify the activity of inflammasome.Results:1.Effect of oridonin on depression-like behavior induced by chronic unpredictable stress.(1)Rats exposed to chronic unpredictability stress for 6 weeks showed significant depressive behavior beginning at the end of third week.(2)Both prophylactic administration and therapeutic administration of oridonin improved depression-like behavior,and the effect of the former was better than the latter.(3)The antidepressant effect of 10 mg/kg oridonin was better than 10 mg/kg fluoxetine,and the effect of their combination was better than the maximum effective dose of fluoxetine,18 mg/kg.(4)All 10 mg/kg oridonin could decrease the activity of microglial cells in prefrontal cortex and hippocampus,especially in the latter.2.Effect of oridonin on abnormal glucose metabolism induced by chronic unpredictable stress.(1)Rats exposed to chronic unpredictability stress for 6 weeks showed significant insulin metabolism abnormalities beginning at the end of fourth week.(2)Oridonin can prevent insulin metabolism and insulin resistance.(3)Oridonin can reduce the infiltration of macrophages into pancreatic tissue,and fluoxetine can reduce the expression of insulin.3.The molecular mechanism by which oridonin influences depression-like behavior and insulin resistance.(1)Oridonin can improve the insulin signal transduction pathway disorder and the expression of IL-1β and IL-18 in the hippocampus.(2)Oridonin can improve the expression levels of IL-1β and IL-18 in peripheral blood and pancreatic tissue,and the increase of corticosterone.(3)Oridonin attenuates the activity of NLRP3 inflammasome by inhibiting the interaction between NEK7 and NLRP3.(4)The expression levels of IL-1β and IL-18 in RAW264.7 and BV2 cells were decreased in a dose-dependent manner by oridonin.Conclusions:In summary,we hypothesize that depression-like behavior may coexist with insulin resistance through the NEK7-NLRP3 inflammasome activation pathway.The results of this study showed that oridonin effectively alleviated depression-like behavior and insulin resistance in CUMS rats by blocking the interaction between NLRP3 and NEK7.In addition,the antidepressant effect of oridonin combined with fluoxetine was significantly better than that of high-dose fluoxetine alone.It is worth noting that oridonin is an effective adjuvant for enhancing the antidepressant effects of fluoxetine,but there may be a dose ceiling effect in antidepressant therapy.Therefore,our results reveal a novel role of oridonin and provide a more effective drug therapy strategy for the treatment of depression with insulin resistance. |
