Paeoniflorin suppresses allergic and inflammatory responses by promoting autophagy in rats with urticaria

Abstract

Paeoniflorin (PF) has been reported to be effective against several skin disorders, such as allergic contact dermatitis and psoriasis; however, it remains unclear whether PF can protect against urticarial lesions. Herein, the effects of PF on rats with urticarial lesions and the possible underlying mechanism were investigated. The effects of PF administration on a rat model of ovalbumin-induced urticarial-like lesions were evaluated via pathological analysis using hematoxylin-eosin staining. Toluidine blue staining was performed to detect mast cells and ELISA was performed to determine serum histamine levels. PF-induced regulatory effects on autophagic activity and the potential underlying mechanism of this were also investigated using transmission electron microscopy, immunohistochemistry and reverse transcription-quantitative PCR. It was demonstrated that PF suppressed allergic and inflammatory responses to improve urticarial lesions, as evidenced by the attenuation of pathological abnormalities, mast cell infiltration and histamine secretion. Mechanistically, PF treatment was found to markedly limit the production and release of inflammatory cytokine interleukin (IL)-23, while the levels of IL-17 remained unchanged. PF intervention led to an increased number of autophagosomes, along with higher levels of light chain 3B (LC3B) and Beclin-1, and lower levels of P62, indicating that PF could augment autophagic activity in urticarial lesions. PF treatment increased the expression of liver kinase B1 (LKB1) and AMP-activated protein kinase-α (AMPK-α), contributing to the PF-enhanced autophagic activity. In conclusion, PF could effectively improve urticarial lesions by inhibiting inflammatory cytokine IL-23 and increasing the autophagic activity via the LKB1/AMPK-α pathway.

Keywords: allergy; autophagy; inflammation; paeoniflorin; urticaria.

Figure 1

PF ameliorates histopathological abnormalities in rats with urticaria. Dorsal skin obtained from normal, model urticarial and LOR and PF-treated rats with urticaria were stained using hematoxylin and eosin (magnification, x100 and x400). PF, paeoniflorin; LOR, loratadine.

Figure 2

PF inhibits mast cell infiltration and degranulation in rats with urticaria. (A) Representative images of toluidine blue-stained mast cells in dorsal skin tissue (magnification, x100). (B) Number of mast cells in the dermis (n=10). ^**P<0.01 vs. normal group; ^##P<0.01 vs. model group. Data are presented as the mean ± SD. PF, paeoniflorin; LOR, loratadine.

Figure 3

PF decreases serum histamine level in rats with urticaria. ^**P<0.01 vs. normal group; ^##P<0.01 vs. model group. Data are presented as the mean ± SD (n=10). PF, paeoniflorin; LOR, loratadine.

Figure 4

Effects of PF on IL-23 production in rats with urticaria. (A) Representative IHC images showing IL-23 expression in dorsal skin sections from each group (magnification, x100). (B) Semi-quantitative analysis of IL-23 protein expression using IHC (n=10). (C) Reverse transcription-quantitative PCR of IL-23 mRNA levels in each group (n=6). ^**P<0.01 vs. normal group; ^#P<0.05 and ^##P<0.01 vs. model group; ^▲▲P<0.01 vs. model + LOR group. Data are presented as the mean ± SD. PF, paeoniflorin; IL, interleukin; IHC, immunohistochemistry; LOR, loratadine; IOD, integrated optical density.

Figure 5

PF enhances autophagic activity in rats with urticaria. (A) Representative transmission electron microscopy images illustrating autophagosomes (red arrows) and (B) semi-quantitative analysis of autophagosomes in each group (magnification, x12,000) (n=6). ^**P<0.01 vs. normal group; ^##P<0.01 vs. model group; ^▲▲P<0.01 vs. model + LOR group. Data are presented as the mean ± SD. PF, paeoniflorin; LOR, loratadine; N, nucleus; M, mitochondrion; ER, endoplasmic reticulum; GC, golgi complex.

Figure 6

Effects of PF on Beclin-1, LC3B and P62 in rats with urticaria. (A) Representative IHC images showing the expression of Beclin-1, LC3B and P62 in dorsal skin sections from each group (magnification, x100). Semi-quantitative analysis of (B) Beclin-1, (D) LC3B and (F) P62 protein expression using IHC (n=10). Reverse transcription-quantitative PCR of (C) Beclin-1, (E) LC3B and (G) P62 mRNA levels in each group (n=6). ^*P<0.05 and ^**P<0.01 vs. normal group; ^#P<0.05 and ^##P <0.01 vs. model group; ^▲P<0.05 and ^▲▲P<0.01 vs. model + LOR group. Data are presented as the mean ± SD. PF, paeoniflorin; LC3B, light chain 3B; IHC, immunohistochemistry; LOR, loratadine.

Figure 7

Effects of PF on LKB1 and AMPK-α in rats with urticaria. (A) Representative IHC images showing the expression of LKB1 and AMPK-α in dorsal skin sections from each group (magnification, x100). Semi-quantitative analysis of (B) LKB1 and (D) AMPK-α protein expression using IHC (n=10). Reverse transcription-quantitative PCR of (C) LKB1 and (E) AMPK-α mRNA levels in each group (n=6). ^**P<0.01 vs. normal group; ^#P<0.05 and ^##P<0.01 vs. model group; ^▲P<0.05 and ^▲▲P<0.01 vs. model + LOR group. Data are presented as the mean ± SD. PF, paeoniflorin; LKB1, liver kinase B1; AMPK-α, AMP-activated protein kinase-α; IHC, immunohistochemistry; LOR, loratadine.