Inhibitory effects of total flavones of buckwheat flower on the non-enzymatic glycation of proteins in vivo and in vitro

Fengling NIU; Jinxiu CHU; Shuying HAN

ABSTRACT

BACKGROUND:

Non-enzymatic glycation of proteins is involved in the complications of diabetes mellitus. Previous experiments have demonstrated that total flavones of buckwheat flower (TFBF) could improve carbohydrate tolerance. However, it is little known whether TFBF inhibit the non-enzymatic glycation of proteins.

OBJECTIVE:

To investigate the influences of TFBF on the non-enzymatic advanced glycation end products (AGEs) of proteins in vivo and in vitro.

DESIGN:

Completely randomized controlled trial.

SETTING:

Department of Pharmacology, North China Coal Medical College.MATERIALS Totally 75 adult SD rats , of clean grade, weighing (200±20) g, including 38 female rats and 37 male rats, were provided by the institute of experimental animals, Chinese Academy of Medical Sciences (Certification No. SCXK11-00-0006). TFBF was extracted by our laboratory from flowers of buckwheat. The blood glucose kit was purchased from Beijing Biosino Biotechnology Company Ltd. Penicillin (Batch No.031020, 8×105 U) and streptomycin (Batch No. 030920, 1×106 U) were purchased from North China Pharmaceutical Company. Streptozotocin and BSA were purchased from Sigma Company. Fructosamine kit was purchased from Nanjing Jiancheng Bioengineering Institute, and the other chemicals were analytical pure produced domestically.

METHODS:

This experiment was carried out in the Department of Pharmacology, North China Coal Medical College from March to October 2004.In the first experiment, in vivo macromolecular AGEs was measured ①Modeling and grouping Rats were divided into 3 groups according to body mass Normal control group (n=15), the rats were treated with 8 mL/kg normal saline intraperitoneally. Streptozotocin-treated group (n=45), the rats were fasted for 16 hours and then treated with 80 mg/kg streptozotocin of 8 mL/kg intraperitoneally. Twenty-two hours later, the blood of all rats was harvested from vena caudalis to measure the level of blood sugar.Those with fasting blood glucose ≥ 15 mmol/L were acted as diabetic rats.Streptozotocin-treated group were divided into 3 subgroups, 15 rats in each subgroups. Each rat was given intragastric administration of 0.1, 0.2 and 0.4 g/kg TFBF. Model group (n=1S) Rats were only treated with 80 mg/kg streptozotocin of 8 mL/kg . The rats in normal control group and model group were given the same volume of salt water. The administration was once a day for 12 weeks successively. ②Measurement of fasting blood glucose After the last administration, the rats of streptozotocin-treated group were fasted for 12 hours and the blood was harvested from vena caudalis. The fasting blood glucose was measured by glucose oxidase method. ③The levels of blood plasma and nephridial tissue fructosamine and macromolecular AGEs were measured The rats of each group were anesthetized with ethyl ether on the second day following the last administration. Blood was chosen from carotid artery, and plasma was separated.Kidneys were taken at the same time, prepared into 100 g/L tissue homogenate and centrifuged at low temperature. The levels of fructosamine in plasma and the supernatant fluid of kidney homogenate were measured according to the instructions of the kit. AGEs in plasma and renal tissue were determined by fluorospectrophotometer. The products of macromolecular AGEs were calculated. In the second experiment, in vitro macromolecular AGEs were measured as below 0.01, 0.05, 0.10 mg/L TFBF of 6 mLrespectively was prepared with solution A (0.2 mol/L glucose, 2×l06 U/Lpenicillin, 2×106 U/L streptomycin , PBS containing 20 g/L bovine serum albumin). Control groups were set ① without TFBF, ② without TFBF and glucose, ③ without BSA, ④ without glucose. Five parallels of each sample were sterilized by filtration and incubated in the attemperator at 37 ℃. The fluorescence of AGEs (F) in the culture was determined at the 4th, 8th and 12th weeks. Inhibition ratio (IR) was calculated and the inhibition of TFBF on AGEs was observed.MAIN OUTCOME

MEASURES:

In the first experiment, the levels of fasting blood glucose, fructosamine in kidney and plasma, and AGEs were measured. In the second experiment, the inhibition of TFBF on AGEs in vitro was measured.

RESULTS:

In the first experiment, 75 rats were involved, and 56 successful rats entered the stage of result analysis. The levels of blood glucose,fructosamine in kidney and plasma of rats in the model group were significantly higher than those of rats in the normal control group (t=7.572,10.186, 5.794,P ＜ 0.01 ). The level of blood glucose of rats in the 3 subgroups was significantly lower than that of rats in the model group (t=3.357,4.382,3.938,P ＜ 0.05-0.01); The levels of fructosamine in kidney and plasma of rats in the 0.2 and 0.4 g/kg TFBF groups were significantly lower than those in the model group (t=5.109, 4.605, 3.731,3.097,P ＜ 0.05-0.01 ). The levels of AGEs in plasma and kidney of rats in the model group were significantly higher than those in the normal control group (t=6.463, 12.704,P ＜ 0.01 ), while the levels of AGEs in plasma of rats in the streptozotocin-treated group were similar to those in the model control group (P ＞. 0.05), and those in kidney of rats in the streptozotocintreated subgroups were significantly lower than those in the model group (t=9.845, 12.799, 12.899,P ＜ 0.01 ). In the second experiment, the level of macromolecular AGEs of each group was gradually increased with ime.TFBFcould inhibit the formation of macromolecular AGEs in dose- and time-dependent manner.

CONCLUSION:

TFBF obviously inhibited the formation of AGEs of proteins in vivo and in vitro.