Figure 1.

D-4F inhibits capsaicin-induced mechanical and thermal hyperalgesia independent of TRPV1 activation. (a–c) Measurements of mechanical paw pressure threshold by Randall–Selitto and paw withdrawal thresholds by von Frey test as well as thermal paw withdraw latency by Hargreaves test before (0) and 1, 3, and 6 h after intraplantar injection of capsaicin (245 nM) plus subsequent application of D-4F (2.5 mg/kg i.p.) or vehicle in male Wistar rats. Filled symbols indicate D-4F; open symbols for vehicle treatment groups. N as indicated in the graphs. Two-way repeated-measurement ANOVA, post hoc Holm–Sidak; *P < 0.05 highlighting significant differences between treatments at indicated time points. (d and e) Representative traces of calcium transients in Fura-2-based calcium imaging experiments on HEK-293_TRPV1 cells upon stimulation with capsaicin alone (1 µM) or a pre-incubated mixture with D-4F (100 μg/ml; 30 min). Grey lines: individual cells, black line: mean; indicator line in (d) highlights interval chosen for AUC calculations. (f and g) Statistical analysis of the area under curve (interval: 120–390 s) and the number of responding cells upon stimulation. Scatter dot plots including median with interquartile ranges. Filled symbols indicate D-4F application; open symbols for vehicle treatment groups. N = 4 independent experiments of averaged duplicates. Mann–Whitney U test. *P < 0.05. 4-HNE: 4-hydroxynonenal; H₂O₂: hydrogen peroxide; D-4F: D-amino-4-phenylalanine mimetic peptide of apolipoprotein A-I.