Effect Of Dexamethasone On The T.gondii Proliferation And Metebolish Of Polyunsaturated Fatty Acid In T.gondii And Host

Background and objective: Toxoplasma gondii（T.gondii）is an apicomplexan obligate intracellular parasite,which can infection people,mammals and birds,causing toxoplasmosis.The majority of human infections are benign and asymptomatic.If immunity was impaired,latent infection would be reactivated causing widespread tissue destruction and severe pathology reactions,the consequences would be more severe especially in AIDS patients and those receiving immunosuppressive therapy or organ transplantation.In recent years,some report suggested that the usage of exogenous corticosteroids would result the experiment animals have more susceptibility to the pathogenic organisms.Patients used Dexamethasone and other glucocorticoid for a long term,would had more chance to outbreak acute toxoplasmosis than those did not.Dexamethasone as a glucocorticoid used widely in clinical,it not only has anti-inflammatory and anti shock effect,but also affect the metabolism of fatty acids.Studies have shown that dexamethasone has a certain effect on the proliferation of T.gondii in rat macrophages,but its mechanism is not clear.Polyunsaturated fatty acid is not only an important component of the cell membrane also involved in some important process of signal transmission of cell growth and development,this paper discusses the effect of dexamethasone on the T.gondii proliferation and metabolism of polyunsaturated fatty acid in T.gondii and host.Methods: 1.MTT assay the effect of DXM on the proliferation of T.gondii RH strain tachyzoite.2.The Giemsa staining was used to observe the infection and intracellular replication of parasite.3.The cell counting was used to assay the effect of dexamethasone on the number of extracellular T.gondii.4.The gas chromatography was used to analysed the effects of dexamethasone on polyunsaturated fatty acid metabolism of T.gondii RH strain tachyzoite and the MDA-MB-231 Cell.Results: 1.The proliferation of T.gondii were promoted by dexamethasone.MTT assay showed that dexamethasone promoted the proliferation of T.gondii,and the promotion was dependent on both dose and time.at first 24 h,there was no significant difference between control and treatment groups（p>0.05）optical density value（ODvalue）of parasites cell.But there were significant difference between control and treatment groups after 48 h.At 72 h,the OD value of parasites cells were 0.4570±0.017,0.5545±0.023,0.6024±0.035,0.6535±0.046,respectively.A statistically significant difference was observed when compared to the control group（0.3505±0.012）（P<0.01）.2.The Giemsa staining showed that the number of tachyzoites of intra-231 cells was increased 497±5,1071±21,4847±115 by a 48 h,60h,72 h treat with 10^-4mg/ml DXM.There was a significant difference when compared to the control group（269 ±7,573±11,1057±42）（P<0.01）.Also,the bigger pseudocysts were found in the experimental group of infected 231 cells.The infected 231 cells number were 65±1,88±2,99±1,100 ±0 per 100 cells in experimental group respectively,at 24 h,48h,60 h,72h,while the control group were 51±3,68±2,83±2,92.3±2.There was a significant difference between the control groups and the experimental groups（p <0.01）.3.The cell counting showed that there were significant difference between control and treatment groups after 48h（p <0.01）.The number of extracellular T.gondii were（18±5,119±16,154±29）×10⁴/ml in experimental group(treat with 10^-4mg/ml DXM)respectively,at 48 h,72h,96 h,while the control group were（17±5,65±10,69±10）×10⁴/ml.4.The result of GC analysis showed that T.gondii had different kinds of fatty acids,including c16:0,c18:0,c18:1,c18:2,c18:3,c20:0,c20:1,c20:2,c20:4,c22:1and c22:2.The most of T.gondii fatty acid were long-chain polyunsaturated fatty acid.While the experimental group T.gondii emerged amount change of fatty acids compared to the control group T.gondii.In the experimental group,the fatty acids metabolism of T.gondii was enhanced remarkably.The amount fatty acids（c18:1）increased remarkably.The 231 cells of infected T.gondii had more polyunsaturated fatty acid,when compared to the 231 cells without infected T.gondii.While the unsaturated fatty acids of experimental 231 cells that infected T.gondii treated with 10^-4mg/ml DXM was similar to the control group 231 cells,and also found the c18:1 increased when compared to the group not treated with DXM.Conclusions: 1.The proliferation of T.gondii were promoted by dexamethasone,and the promotion was dependent on dose.2.The change of fatty acids metabolism of T.gondii RH strain tachyzoite and the MDA-MB-231 Cell was induced by dexamethasone.3.The the mechanism of DXM-induced tachyzoite proliferation presented a new mechanism.The polyunsaturated fatty acid played an important role in the growth of T.gondii tachyzoites.