Capsaicin suppresses interleukin-31-induced itching partially involved in inhibiting the expression of dorsal root ganglion interleukin-31 receptor A in male mice

Abstract

To elucidate the mechanisms underlying the antipruritic effect of capsaicin, we investigated how topical application of capsaicin (0.01, 0.1 and 1.0% w/v) affects spontaneous scratching in NC/Nga mice, inerleukin-31 (IL-31) induced in BALB/c mice, and IL-31 receptor A (IL-31RA) and transient receptor potential vanilloid member 1 (TRPV1) mRNA expression in dorsal root ganglia (DRG). Capsaicin concentration-dependently suppressed long-lasting scratching (over 1.0 s, itch-associated scratching) and short-lasting scratching (0.3-1.0 s, locomotor activity) immediately after the application. Total long-lasting scratching and short-lasting scratching counts for 24 h and IL-31RA mRNA expression in the DRG significantly decreased with increasing concentration of capsaicin. Furthermore, 1.0% capsaicin suppressed long-lasting scratching and short-lasting scratching for more than 72 h. At this point, DRG IL-31RAmRNA was significantly decreased, but there was no change in cutaneous IL-31RA and TRPV1 mRNA. Thus capsaicin suppresses long-lasting scratching by inhibiting IL-31RA mRNA expression in the DRG. Next, we examined the effect of capsaicin on IL-31-induced long-lasting scratching in BALB/c mice. Repeated administration of IL-31 (50 μg/kg, subcutaneous) every 12 h for 3 days apparently increased long-lasting scratching counts and IL-31RA mRNA in the DRG. These increases were significantly suppressed by pretreatment with 1.0% capsaicin. TRPV1 mRNA in the DRG was also decreased within 1-24 h after capsaicin application. These results suggest that the strong and prolonged antipruritic action for IL-31-induced itching of capsaicin was caused by desensitization of C-fibers, and, in addition, the long-lasting inhibition of IL-31RA mRNA expression in the DRG.

Keywords: AD, Atopic dermatitis; Capsaicin; DRG, dorsal root ganglia; IL-31 receptor A (IL-31RA); IL-31, Interleukin-31; IL-31RA, Interleukin-31 receptor A; Interleukin-31 (IL-31); Itch; TRPV1, transient receptor potential vanilloid member 1; Transient receptor potential vanilloid member 1 (TRPV1).

Fig. 1

Effect of topically applied capsaicin on spontaneous scratching behavior of skin-lesioned NC/Nga mice (A) Typical intra-day pattern outlining the inhibitory effect of topically applied capsaicin (0.01, 0.1 and 1.0% w/v) on long-lasting scratching of NC/Nga mice. The blue line indicates the vehicle- treated group; red line indicates the 0.01% capsaicin-treated group; yellow line indicates the 0.1% capsaicin treated-group; green line indicates the 1.0% capsaicin treated-group. The red arrow indicates the application of vehicle or capsaicin. The yellow arrow indicates the sampling point of PCR for Fig. 2. Data represent scratching counts at each hour. The lateral axis indicates the clock hour, and the shaded area represents the dark phase (7:00 pm to 7:00 am). (B) Typical intra-day inhibition pattern of topically applied capsaicin on short-lasting scratching (social behavior) of NC/Nga mice. (C) The total long-lasting scratching counts for 24 h of capsaicin. The blue column indicates vehicle treated group; the red column indicates 0.01% capsaicin-treated group; the yellow column indicates 0.1% capsaicin-treated group; the green column indicates 1% capsaicin-treated group. (D) Total short-lasting scratching counts after 24 h applying capsaicin for 24 h. Each value represents the mean ± SE from six mice. NS, not significant, **P < 0.01 when compared with the vehicle-treaed (0) group (Dunnett test). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

Dose dependent inhibitory effect of topically applied capsaicin on IL-31RA mRNA expression in NC/Nga mice (A) IL-31RA mRNA expression in the dorsal root ganglia (DRG). The blue column indicates the vehicle- treated group, the red column indicates the 0.01% capsaicin-treated group, the yellow column indicates the 0.1% capsaicin-treated group, the green column indicates the 1.0% capsaicin-treated group. (B) correlation 1: correlation between the IL-31RA mRNA expression in the DRG and long-lasting scratching in skin-lesioned NC/Nga mice. (C) correlation 2: correlation between the IL-31RA mRNA expression in the DRG and short-lasting scratching in skin-lesioned NC/Nga mice. Each value represents the mean ± SE from four mice. NS, not significant, **P < 0.01 when compared with the vehicle treated (0) group (Dunnett test). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

Effect of administering high concentration of capsaicin 72 h after topically application on spontaneous scratching behavior and on cutaneous and IL-31RA and IL-31RA and TRPV1 mRNA expression in the DRG in skin-lesioned NC/Nga mice (A) Total long-lasting scratching and (B) short-lasting scratching counts of vehicle and capsaicin treated group. The blue column indicates the vehicle-treated group. The red column indicates the 1.0% capsaicin-treated group. Day 0 indicates the time before vehicle or capsaicin treatment, while day 1, 2, 3 indicates 0–24 h, 24–48 h, 48–72 h, respectively, after vehicle or capsaicin treatment in each group. The yellow arrow indicates the sampling point of PCR for Fig. 3C - E. Each value represents the mean ± SE from six mice. NS, **P < 0.01 and ***P < 0.001 when compared with the vehicle treated group (Student’s t test). (C) IL-31RA mRNA in the DRG. (D) Expression of cutaneous IL-31RA mRNA. (E) TRPV1 mRNA in the DRG. The green column indicates non-treated group, the blue column indicates vehicle-treated group, the red column indicates 1.0% capsaicin-treated group. *P < 0.01 when compared with the vehicle (ethanol: EtOH) treated group (Tukey’s test). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 4

Effect of topically applied 1.0% capsaicin on IL-31-induced itch-associated scratching behavior (long-lasting scratching) in BALB/c mice. (A) Long-lasting scratching induced by IL-31 was measured for 96 h in BALB/c mice. The black arrow indicates the site of injection of the vehicle or IL-31 (50 μg/kg, subcutaneous) every 12 h (7:00 am and 7:00 pm) for 96 h. The lateral axis indicates the clock hour, and the shaded area represents the dark phase (7:00 pm to 7:00 am). The red arrow indicates the site of topical application of the vehicle or capsaicin. The blue line indicates saline + vehicle-treated group, the yellow line indicates saline + capsaicin treated group; the red line indicates IL-31 + vehicle-treated group; the green line indicates the IL-31 + capsaicin-treated group. (B) Total long-lasting scratching counts measured 24 h before administering IL-31 (day 0) and on day 1 (0–24 h), day 2 (25–48 h), day 3 (48–72 h), day 4 (72–96 h) and day 5 (96–120 h) after administering IL-31. The blue column indicates saline + vehicle-treated group, the yellow column indicates saline + capsaicin treated group; the red column indicates IL-31 + vehicle-treated group; the green column indicates IL-31 + capsaicin-treated group. Each value represents the mean ± SE from six mice. **P < 0.01 and ***P < 0.001 compared with the respective values in the same-day group. (Tukey’s test). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 5

Effect of topically applied 1.0% capsaicin on IL-31-induced locomotor activity in BALB/c mice. (A) Short-lasting scratching induced (locomotor activity) by IL-31 was measured for 96 h in BALB/c mice. The black arrow indicates the site of injection of the vehicle or IL-31 (50 μg/kg, subcutaneously) every 12 h (7:00 am and 7:00 pm) for 96 h. The lateral axis indicates the clock hour, and the shaded area represents the dark phase (7:00 pm to 7:00 am). The red arrow indicates the site of topical application of the vehicle or capsaicin. The blue line indicates saline + vehicle-treated group, the yellow line indicates saline + capsaicin treated group; the red line indicates IL-31 + vehicle-treated group; the green line indicates the IL-31 + capsaicin-treated group. (B) Total short-lasting scratching counts measured 24 h before administering IL-31 (day 0) and on day 1 (0–24 h), day 2 (25–48 h), day 3 (48–72 h), day 4 (72–96 h) and day 5 (96–120 h) after administering IL-31. The blue column indicates saline + vehicle-treated group, the yellow column indicates saline + capsaicin treated group; the red column indicates IL-31 + vehicle-treated group; the green column indicates IL-31 + capsaicin-treated group. Each value represents the mean ± SE from six mice. **P < 0.01 and ***P < 0.001 compared with the respective values in the same-day group. (Tukey’s test). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 6

Time course of the changes in the expression of cutaneous IL-31RA mRNA and IL-31RA and TRPV1 mRNA expression in the DRG of 1.0% capsaicin treated BALB/c mice. Expression of cutaneous (A) IL-31RA mRNA (cIL-31RA). (B) IL-31RA mRNA in the DRG (dIL-31RA) and (C) TRPV1 mRNA in the DRG (dTRPV1). (D) Pain threshold after capsaicin application measured using hot-plate test. (E) Correlation between the latency and expression of TRPV1 mRNA in the DRG. The blue line indicates the vehicle (ethanol)-treated group, while the red line indicates 1.0% capsaicin-treated group. Each value represents the mean ± SE from six mice. N.S., not significant. * P < 0.05, **P < 0.01 and ***P < 0.001 compared with the corresponding values of vehicle-treated group (Student’s t test). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)