Study On The Effects Of Fluoxetine On Hepatic Lipid Metablism

The widely used antidepressants, especially such selective serotonin reuptakeinhibitors (SSRIs) as fluoxetine, have high propensity to induce metabolic disorderssuch as weight gain and dyslipidemia in patients. Even though the lipid-relatedeffects of fluoxetine have been attributed to the change of appetite by taking effect ontargets in central nervous system, mechanisms of weight gain resulting fromfluoxetine treatment are still far from fully addressed. The objective of the presentstudy is to investigate the peripheral mechanisms of the metabolic side effects offluoxetine. Adult male mice and primary cultured mouse hepatocytes were treatedwith various concentrations of fluoxetine. Staining with Oil Red O was used toobserve the accumulation of neutral lipids. The expression of genes which areinvolved in lipid metabolism was determined by RT-PCR and Western blottinganalysis respectively. In results, lipid accumulation both in mouse livers (in vivo)and hepatocytes (in vitro) was significantly increased by fluoxetine. Furthermore,the expression of acetyl-CoA carboxylase1(ACC1) and fatty acid synthase (FAS),which were the critical enzymes of fatty acid synthesis, was evidently elevated. Onthe contrast, the expression of triacylglycerol hydrolases, carboxylesterase1(CES1)and carboxylesterase3(CES3), both in mouse livers and hepatocytes, was sharplysuppressed by fluoxetine. Meanwhile, the activation of Sterol regulatory element-binding protein1c (SREBP1c), a lipid-modulating transcription factor which effects asthe upstream of enzymes of fatty acid synthesis, was also stimulated by fluoxetine.What is more, the expression of AMPK (AMP activated protein kinase) wasdownregulated by fluoxetine in vitro, and AICAR, which is an activator of AMPK,abolished the activation of SREBP1c and the upregulation of ACC1induced byfluoxetine. These data suggest that fluoxetine treatment obviously upregulateslipogenesis via activating SREBP1c which may relate to the regulation of AMPKpathway, as well as downregulates lipolysis in vivo and in vitro, resulting insignificantly lipid accumulation in liver. This study provides new insight into the understanding of the mechanisms for SSRI-mediated weight gain and dyslipidemiaeffects.Part I: Fluoxetine induces lipid accumulation in mice liversTo investigate the effects of fluoxetine on the lipid metabolism in mouse liver.All mice except controls received an intraperitoneal injection of fluoxetine10mg/kgor25mg/kg. The mice were sacrificed at24h after fluoxetine treatment. Liverneutral lipid was determined by oil red O. Liver triglyceride and total cholesterolwere measured by test kit. Liver SREBP1c, ACC1and FAS as well as CES1andCES3protein levels were determined by Western Blot.This study demonstrated for the first time that acute fluoxetine treatment inducedhepatic lipid accumulation in mouse liver. Furthermore, the expression of ACC1and FAS was evidently elevated while the expression of triacylglycerol hydrolases,CES1and CES3was suppressed by fluoxetine. Meanwhile, the activation ofSREBP1c, a lipid-modulating transcription factor, was also stimulated by fluoxetine.These data suggest that fluoxetine may upregulates lipogenesis via SREBP1c, aswell as downregulates lipolysis, resulting in liver lipid accumulation.Part II: Fluoxetine induces lipid accumulation in primarymice hepatocytesThrough the study of the first part, we found that fluoxetine induced lipidaccumulation in mouse liver. To exclude the effect of fluoxetine in central nervoussystem, and investigate the direct effects of fluoxetine on the lipid metabolism inmouse liver, we cultured primary mouse hepatocytes, and then observed the effect offluoxetine on primary mouse hepatocytes.Cells were treated with an increasing concertrition of fluoxetine (0,2.5,10and25μM) for24h. Hepatocytes neutral lipid was determined by oil red O. Theexpression of SREBP1c, ACC1, and FAS, AMPK protein levels were determined byWestern Blot. The mRNA and protein levels of CES1and CES3were measured. Primary mouse hepatocytes were pretreated with AICAR, and continuousely sufferedfrom fluoxetine. The expression of ACC1and the activation of SREBP1c weredetermined by Western Blot.This study demonstrated that fluoxetine treatment directly induced hepatic lipidaccumulation in primary mouse hepatocytes. Furthermore, the expression of ACC1and FAS was evidently elevated while the expression of triacylglycerol hydrolases,CES1and CES3was suppressed in a concertrition-dependent manner after treatmentof fluoxetine. Meanwhile, the expression of SREBP1c, a lipid-modulatingtranscription factor, was also activated by fluoxetine in a concertrition-dependentmanner. What is more, the expression of AMPK was downregulated and AICAR,which is an activator of AMPK, abolished the activation of SREBP1c and theupregulation of ACC1induced by fluoxetine.These data suggest that fluoxetine may upregulates lipogenesis via the activationof SREBP1c which related to AMPK pathway, as well as downregulates lipolysis inprimary mouse hepatocytes, resulting in hepatic lipid accumulation.