Effects Of 6-gingerol On 5-HT Synthesis,Metabolism,Transport And 5-HT₃ Receptors In Chemotherapy Rats

Purpose:This study is designed to observing effects of 6-gingerol on pica and 5-HT levels in rats after chemotherapy and investigate 6-gingerol’s antiemetic mechanism by focusing on the synthesis,metabolism and reuptake of 5-HT,as well as the mechanism of 5-Hydroxytryptamine type 3 receptor（5-HT₃ receptor）,in a cisplatin-induced pica model of rats.Methods:The rats were randomly divided into seven groups with eight rats in each group,that is group A was the normal control group,group B was the 6-gingerol control group,group C was the ondansetron control group,group D was the cisplatin model group,group E was the ondansetron-treated group,group F was the high dosage of 6-gingerol-treated group,and group G was the low dosage of 6-gingerol-treated group.The rats of group B,F and G were administered with 6-gingerol with 50mg/kg,50mg/kg and 100mg/kg,respectively.The rats of group C and E were administered with ondansetron with 2.8 mg/kg,respectively.The rats of group A and D were administered with vehicle（3% Tween-80）,respectively.The above dose was given twice one day（7:00 AM and 7:00 PM）.One hour after the first treatment（8:00 AM）,groups D,E,F and G were injected intraperitoneally（i.p.）with 6mg/kg cisplatin,while groups A,B and C were injected i.p.with saline of equal volume.The general conditions of the rats were closely observed,including physical activity,fur,appetite,breathing,and stool.The consumption of kaolin,food and body weight of the rats were measured both before and after cisplatin injection.The levels of 5-HT and its metabolite 5-HIAA in ileum,medulla oblongata and serum were determined using HPLCECD.The m RNA expression levels of 5-HT₃ receptor,tryptophan hydroxylase（TPH）,monoamine oxidase A（MAOA）and serotonin reuptake transporter（SERT）were detected by real-time PCR.The protein expression levels and distribution of 5-HT₃ receptor,TPH and MAOA in the medulla oblongata and ileum were measured by Western blotting and immunohistochemistry respectively.Results: 1.Effects of 6-gingerol on kaolin consumption in chemotherapy ratsThe kaolin intake of rats injected i.p.with cisplatin was significantly increased compared with the normal control group（P<0.001）.Kaolin consumption in the 6-gingerol-treatment groups was significantly decreased（P<0.01,P<0.05）.2.Effects of 6-gingerol on 5-HT Levels in chemotherapy ratsThe levels of 5-HT in serum,medulla oblongata,and ileum of rats treated with cisplatin was significantly increased in comparison to the normal control group（P<0.05）.Compared to the cisplatin model group,the rats treated with 6-gingerol had a reduction in 5-HT levels,although statistical significance was only observed for treatment with high and low dosages of 6-gingerol in medulla oblongata（P<0.01）and of high dosage of 6-gingerol in ileum（P<0.05）.3.Effects of 6-gingerol on expression levels of TPH,MAO-A,SERT,and 5-HT₃ receptor in ileum and medulla oblongata of chemotherapy rats 1)m RNA expressionAfter cisplatin administration,m RNA expression of TPH1 in ileum,TPH2 in medulla oblongata and 5-HT₃ receptor in medulla oblongata and ileum were significantly increased,compared to the normal control group（P<0.05）.6-gingerol significantly downregulated m RNA expression TPH1,TPH2 and 5-HT₃ receptor as compared to the cisplatin control（P<0.05）.Cisplatin administration significantly reduced m RNA expression of MAOA and SERT in ileum and medulla oblongata,compared to the normal control group（P<0.05）.6-gingerol significantly increased m RNA expression of MAOA and SERT in ileum when compared to the cisplatin model group（P<0.05）.2)Protein expressionAfter cisplatin administration,protein expression of TPH1 in ileum,TPH2 in medulla oblongata and 5-HT₃ receptor in medulla oblongata and ileum were significantly increased,compared to the normal control group（P<0.05）.6-gingerol significantly downregulated protein expression TPH1,TPH2 and 5-HT₃ receptor as compared to the cisplatin control（P<0.05）.Cisplatin administration significantly reduced protein expression of MAOA in ileum and medulla oblongata,compared to the normal control group（P<0.05）.6-gingerol significantly increased protein expression of MAOA in ileum when compared to the cisplatin model group（P<0.05）.3)immunostaining expressionAfter cisplatin administration,immunostaining expression of TPH1 in ileum,TPH2 in medulla oblongata and 5-HT₃ receptor in medulla oblongata and ileum were significantly increased,compared to the normal control group（P<0.05,P<0.01）.6-gingerol significantly downregulated immunostaining expression TPH1,TPH2 and 5-HT₃ receptor as compared to the cisplatin control（P<0.01）.Cisplatin administration significantly reduced immunostaining expression of MAOA in ileum and medulla oblongata,compared to the normal control group（P<0.01）.6-gingerol significantly increased immunostaining expression of MAOA in ileum when compared to the cisplatin model group（P<0.01）.Conclusion:6-gingerol can inhibit chemotherapeutic pica,suggesting that it has the effect of preventing and treating chemotherapeutic nausea and vomiting,and its mechanism may be related to reducing the level of 5-HT by inhibiting synthesis or accelerating 5-HT degradation during chemotherapy treatment.