[Effect and mechanism of bamboo leaf flavonoids on depression in type 2 diabetic rats]

Objective: To explore the effect and mechanism of bamboo leaf flavonoids on depression in type 2 diabetic rats. Methods: The streptozotocin (STZ) was used to induce the depression model of type 2 diabetic rats. Eight weeks old male Sprague-Dawley (SD) rats were randomly divided into 5 groups: the normal control group (n=8), the model group (n=9), the bamboo leaf flavonoid group (n=9), the solvent control group (n=9) and the bamboo leaf flavonoid normal control group (n=8). Rats of the bamboo leaf flavonoid group and the bamboo leaf flavonoid normal control group were treated with intragastric administration of bamboo leaf flavonoids (200 mg·kg(-1)·d(-1)) for 12 weeks. Tail suspension test (TST) and forced swimming test (FST) were used to measure the level of depression. Nissl staining was used to detect the survival amount of hippocampus neurons. The levels of interleukin-1β (IL-1β) and interleukin-6 (IL-6) were detected by enzyme-linked immunosorbent assay (ELISA). The expression levels of receptor of advanced glycation endproducts (RAGE), phosphorylated signal protein P38 (p-P38), cleaved caspase-3 and the nuclear factor-κB (NF-κB) were detected by Western blotting. Results: Compared with the normal control group, the TST and FST immobility time of the model group rats increased [(206±13) s vs (101±9) s, (192±24) s vs (98±8) s, both P<0.01]. Furthermore, the injury of hippocampal neurons was more severe, and the boundary was unclear. The nissl bodies were scarce or disappeared, and nuclear pyknosis was observed. The levels of hippocampal CA3 IL-1β and IL-6 elevated [(31.78±4.12) pg/ml vs (9.26±3.52) pg/ml, (49.15±3.47) pg/ml vs (19.63±2.18) pg/ml, both P<0.01]. The Western blotting showed that the expressions of RAGE, p-P38, cleaved caspase-3 enhanced and NF-κB nuclear translocation increased (all P<0.05). After bamboo leaf flavonoids treatment (for 12 weeks), compared with the model group, the immobility time of TST and FST reduced in the bamboo leaf flavonoid group [(152±11) s vs (206±13) s, (110±19) s vs (192±24) s, P<0.01], and hippocampal neuronal injury alleviated. In addition, the concentrations of IL-1β and IL-6 decreased [(21.79±3.95) pg/ml vs (31.78±4.12) pg/ml, (34.68±4.28) pg/ml vs (49.15±3.47) pg/ml, both P<0.01] and the expressions of RAGE, p-P38, nuclear NF-κB, cleaved caspase-3 up-regulated in the bamboo leaf flavonoid group. Conclusion: Bamboo leaf flavonoids can effectively improve depression in diabetic rats through decreasing hippocampal neuronal injury and the release of inflammatory factors, and inhibiting RAGE/P38/NF-κB signaling pathway.