Figure 8.

The roles of oxidative stress in itch induced by intradermal injection of MGO and in STZ-induced diabetic mice. (A-B) Flow cytometry (A) and quantification (B) revealed that incubation of MGO (1 mM) increased intracellular ROS in ND7-23 cells, which was inhibited by pre-incubation of antioxidant PBN (200 μM) (n = 4-5 for each group, ^**P < 0.01, ^***P < 0.001 compared with corresponding groups, Student's t test). (C) I.p. injection of antioxidants NAC (200 mg/kg) and PBN (100 mg/kg) significantly decreased MGO (3 μmol)-induced scratching in 30 min (n = 5-7 for each group, ^**P < 0.01, ^***P < 0.001 compared with VEH group, Student's t test). (D) I.p. injection of another antioxidant ALA (100 mg/kg) also decreased MGO (3 μmol)-induced scratching within 30 min (n = 5-8 for each group, ^***P < 0.001 vs. VEH group, Student's t test). (E) Local co-administration of ALA (100-300 μg) dose-dependently decreased MGO (3 μmol)-induced scratching in 30 min (n = 7-8 for each group, ^** P < 0.01 compared with VEH group, one-way AVOVA followed by post-hoc Dunnett's test). (F) I.p. injection of antioxidant ALA (100 mg/kg) also decreased MGO (3 μmol)-induced mechanical itch in mice (n = 5-7 for each group, ^***P < 0.001 compared with VEH group, Student's t test). (G) Co-administration of ALA (100-300 μg) dose-dependently decreased MGO (3 μmol)-induced mechanical itch in mice (n = 5-7 for each group, ^**P < 0.05, ^**P < 0.01 compared with VEH group, one-way AVOVA followed by post-hoc Dunnett's test). (H) Mechanical itch was suppressed by i.p. injection of ALA (100 mg/kg) in STZ-induced diabetic mice (n = 7-10 for each group, ^***P < 0.001 compared with NS group, Student's t test). All data are expressed by means ± SEM. ALA, α-lipoic acid; MGO, methylglyoxal; NS, normal saline; PBN, N-tert-butyl-a-phenylnitrone; PBS, phosphate buffer saline; STZ, streptozotocin; VEH, Vehicle.