| Objective To study the protective effects of GSPE on the cerebral cortex of the STZ induced diabetic rats and the possible mechanisms.Methods 60 Male Wistar rats were randomly divided into 4 groups:normal control group(C1,n=10)and normal control group with GSPE treatment(C2,n=10);the other 40 Wistar rats were used for induction of diabetes,for which a single dose of streptozotocin 55mg/kg was injected into tail veins of the rats.After animal models were successfully established,they were randomly divided into 2 proups:diabetic control group(DM1,n=8) and diabetic group with GSPE treatment(DM2,n=12).Animals were kept in individual cages on a 12-h light-dark cycle with an ambient temperature of 22±1℃,free access to food and water.The care of the animals and research protocols conformed to the guiding principles for animal experimentation as expounded by the Chinese Council on Animal Care and approved by the Animal Care Committee of Shandong University.24 weeks later,cerebral cortexes from experimental rats were separated for morphological observations;reverse transcriptase coupled to polymerase chain reaction(RT-PCR)was employed for quantitative determination of mRNA for RAGE and NF-κB;western blot was used for the determination of protein expression for RAGE and NF-κB.;cerebral cortexes from experimental rats were immunohistochemically stained for immunoreaction detection of RAGE,NF-κB,GFAP,ICAM-1 and VCAM-1 as wellResults(1)Weight and serum indices:Compared to normal control group,the diabetic group weighed significantly less(t=16.791,P<0.001),while fasting plasma glucose(FPG),HbAlc and AGEs were higher with statistic significance(p<0.01);afer treated with GSPE 250 mg/(kg·d)for 24weeks,serum AGEs in DM2 decreased significantly compared to DM1(t=2.792,P=0.02),but there were no statistic significance in body weght,FPG(21.35±3.59 vs.19.04±3.24mmol/L,t=1.494,p=0.153)and HbAlc; (2)Morphological observations of the cerebral cortex:the number of neurons decreased and degeneration of neurons in diabetic group could be seen under light microscope, while GSPE improved some degenerative changes and increased neuron number in the cerebral cortex in GSPE-treated diabetic rats;(3)The mRNA expression of RAGE and NF-KB in the cerebral cortex:By RT-PCR,the mRNA expression of RAGE and NF-KB in DM1 were up-regulated compared to control group,while GSPE treatment down-regulated the expression of RAGE and NF-κB in DM2 at a daily oral dosage of 250mg/kg.(4)The protein expression of RAGE and NF-KB in the cerebral cortex:By western-blot,the protein expression of RAGE and NF-KB were up-regulated,while GSPE treatment down-regulated the protein expression of RAGE and NF-κB in DM2 at a daily oral dosage of 250mg/kg.(5)Immunohistochemistry:Compared to control group, in DM1 group,the grey value of RAGE,NF-KB,ICAM and VCAM decreased,while the area of positive cells increased;the grey value of GFAP decreased,while the number of positive cells increased.After GSPE treatment,the grey value of RAGE,NF-KB,ICAM and VCAM increased in DM2 group,while the area of positive cells decreased;the grey value of GFAP increased,while the number of positive cells decreased.Conclusions AGEs can cause damage to the cerebral cortex of STZ induced diabetic rats,while GSPE not only decreased serum AGEs of diabetic rats,but also down-regulated the expression of RAGE and NF-κB both at mRNA and protein levels at a daily oral dosage of 250mg/kg.By immunohistochemistry,GSPE also down-regulated the expression of RAGE,NF-κB,GFAP,ICAM-1 and VCAM-1.The study enables us to further understand the neuropathophysiological role that RAGE and NF-κB plays in diabetic encephalopathy,and confirms that GSPE might be used as a therapeutical means in the prevention and treatment of this disorder.But whether the protective effects of GSPE on the cerebral cortex were accompanied by the decreased AGEs in the cerebral cortex itself and the decreased affinity of AGEs and RAGE is uncertain and needs furher investigation.
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