Effects Of Diets With Different Carbohydrate Content On Brain Uptake Of [¹⁸f]-2-Fluoro-2-Deoxyglucose In Rats

ObjectiveTo assess the effects of the diets with different carbohydrate content and differentfeeding time on brain uptake of18F-FDG in rats, and to analyze the mechanisms.Methods150SD rats were randomly divided into three groups with different carbohydratecontent diet after2weeks of the normal diet (50rats/group): lowcarbohydrate(LC), intermediate carbohydrate(IC) and high carbohydrate (HC)(calories provided by carbohydrate:0%、52%、70%, fat:80%、28%、10%, andprotein20%、20%、20%, respectively), each group was divided into five groupsaccording to the different feeding time:1meal,2meals,3days,5days and7days(10rats/feeding time/group).10rats in each feeding time group were then dividedinto two groups (n=5, each): one for the measurement of serum biochemicalindicators(including glucose, free fatty acid, ketone bodies and insulin), and theexpressions of glucose transporter1(GLUT1) and transporter3(GLUT3) in brainby western blotting and immunohistochemistry; another for the detection of theradioactivity of brain and liver by γ radioimmunoassay determinator after theinjection of100μCi of18F-FDG, and further calculation of the value of the ratioof these two tissues in per gram(B/L).Results1.The expressions of GLUT1and GLUT3in brain in LC were higher than those inthe other two groups(P<0.05),and there was no significant difference between thetwo groups of IC and HC(P>0.05).2. For the diet of LC, the expressions of GLUT1and GLUT3gradually increasedwith the increase of feeding time from one meal, two meals, three days to five days,getting to the peak, and then decreased slightly at seven-day group. The expressions of GLUT1、and GLUT3in brain in LC were significant higher thanthose in IC and HC at three-day、 five-day、 seven-day feeding time group,respectively(P<0.05).3.The value of B/L in LC was higher than those in the other two groups(F=15.417，P<0.01), and no significant difference was found between IC and HC(P>0.05).4. The levels of serum glucose and insulin in LC were lower than those in IC andHC (F=34.89P<0.01; F=26.51P<0.01), while the values of FFA and KB in LCwere statistically significant higher than those in the other two groups (F=131.96P<0.01; F=602.47P<0.01). There was no significant difference of thesebiochemical indicators between the groups of IC and HC(P>0.05).5. The value of B/L correlated well with both of the expressions of GLUT1andGLUT3in brain, and they were all negatively correlated with the level of glucoseand insulin, while positively correlated with the values of free fatty acids andketone bodies.ConclusionsThere was no apparent effect on18F-FDG uptake in brain with LC diet for onemeal, even one day. While extending feeding time to three days or more, theuptake increased. Therefore, it is unrealistic to increase the uptake of18F-FDG inbrain by changing the diet in clinical brain functional imaging, and it is alsoimpossible to decrease the brain uptake to improve the ratio of target/non-target(T/NT) in18F-FDG metabolism imaging of brain tumors by changing the content ofcarbohydrate in diet.