Preventive activity on complication progression in diabetic rats10)
In streptozotocin (STZ)-induced diabetic rats, a 3-month administration study indicated that the herbal extract (solid extract of AG Herb MIX) showed a trend to inhibit the increase of serum pentosidine and kidney wet weight. It also had an activity similar to aminoguanidine, which is a therapeutic agent for diabetes complications. For the inhibition of pentosidine formation, it showed the effect at a lower concentration compared with aminoguanidine. Inhibitory activity against diabetes complications as well as anti-aging activity can be expected from the herbal extract.
- After 28 male Slc:SD rats at 5 weeks old (SLC Co., Ltd., Shizuoka, Japan) were acclimated to the environment, a complete randomized design was used to divide them into the following 4 groups with 7 animals per group: control (G1), STZ administrated (G2), herbal extract administrated (G3), and aminoguanidine administrated (G4). After the grouping and 12 hours of fasting, STZ was administered into the tail vein in a single dose (55 mg STZ/kg･body wt, citrate buffer, pH 4.5) to induce diabetes. The rats were fed on powder feed for raising mice and rats (MF) (Oriental Yeast Co., Ltd., Tokyo, Japan). MF was administered to all during the quarantine and acclimation periods. After the administration study began, the test substances were added to the feed. For the G3 and G4 groups, the feed to be administered was prepared by mixing the herbal extract or aminoguanidine at a ratio of 0.2%. For the G1 and G2 groups, MF was administered. The rats were fed ad libitum and had free access to the feed. The amount of intake was measured twice a week from the amount of decreased feed in each cage. The test substances were administered for 12 weeks after the STZ treatment. After 12 weeks since the test substances had been first administered, all surviving animals were anesthetized with pentobarbital sodium and euthanized by exsanguination, and then the organs were removed. The 24-hour urine was collected from each group before and 0, 4, 8, and 12 weeks after the STZ administration. The urinary sugar (GU, electrode method) and urinary protein (TP, turbidimetric or Pyrogallol Red method) were measured. The blood was collected via the jugular vein before and 0, 4, 8, and 12 weeks after the STZ administration, and the blood sugar was measured. For the measurement of the glycation reaction products, the blood was collected via the jugular vein of the rats, and, using the serum fraction after being centrifuged at 3,000 rpm for 10 min, furosine (HPLC), 3-deoxyglucosone (3DG) (HPLC), pentosidine (Pent) (ELISA), and Nε-(carboxymethyl)lysine (CML) (ELISA) were measured.
- The herbal extract and aminoguanidine, which is a therapeutic agent for diabetes complications, were administered to the STZ-induced diabetic rats for 3 months and their inhibitory activities against diabetes complications were compared. As a result, although one animal was killed in a fight among the animals in the same cage, the treatment with STZ of 55 mg/kg･bw was able to induce a distinct diabetic status. It was also confirmed that the STZ treatment increased the amount of Maillard reaction product in the blood. The increase in the amount of serum pentosidine (Pent) and CML in the groups that ingested the herbal extract (G3) or aminoguanidine (G4) was inhibited in comparison with the increase in the group to which the test substances were not administered (G2). Similarly, the increase in kidney weight was also inhibited in G3 and G4 compared with G2. In addition, no enlarged kidney was found in G3 and G4.
Amount of glycation reaction products in the blood after AG Herb MIX or aminoguanidine was administered to STZ-induced diabetic rats for 12 weeks