Abstract: Objective To investigate the effect of thymosin β4 (Tβ4) combined with hydrocolloid dressing on early wound healing and p38 mitogen-activated protein kinase (MAPK) signal transduction pathway in rats with deep Ⅱ degree burn. 
Methods Forty healthy Wister male rats with conventional adaptive feeding were selected as the research subjects. Ten rats were randomly selected as the control group, and the remaining 30 animals were divided into burn group (n=10), Tβ4+hydrocolloid dressing group (n=10) and p38MAPK agonist group (n=10) according to the random number table method. Except the control group, the remaining rats were made into deep Ⅱ degree burn models for subsequent experiments. The Tβ4+ hydrocolloid dressing group was given external application of 6 μg Tβ4+ Ampu patch, the p38MAPK agonist group was given external application of 6 μg Tβ4 + AMP patch + external application of p79350 (1 μg/kg), and the burn group was given an equal amount of 0.9% sodium chloride solution for external application. The wounds were photographed on the 3rd, 7th, 10th, and 14th days of administration, and the pictures were processed by MoticMed6 software and Photoshop software;the early wound healing rates of the rats in each group were calculated. The levels of inflammatory factors tumor necrosis factor-α (TNF-α), interleukin-10 (IL-10) in the wound were detected by immunohistochemistry, and reverse transcription-polymerase chain reaction (RT-PCR) was used to detect the expression of transforming growth factor β1 protein (TGF-β1) mRNA and vascular endothelial growth factor (VEGF) mRNA expression in wounds. Western blot (WB) was used to detect the expression of key proteins of p38MAPK signaling pathway p38MAPK, nuclear factor kappa B (NF-κB), cysteine protease 3 (caspase-3). 
Results At 3, 7, 10 and 14 d after administration, the wound healing rate of Tβ4+ hydrocolloid dressing group was higher than that of burn group and p38MAPK agonist group (P＜0.05). Compared with the control group, the levels of TNF-α and IL-10 at each time point in the burn group, Tβ4+hydrocolloid dressing group and p38MAPK agonist group were higher (P＜0.05). At 12, 24, and 48 h after administration, the levels of TNF-α in the burn group and p38MAPK agonist group were higher than those in the Tβ4+hydrocolloid dressing group (P＜0.05), while the IL-10 level was lower than that in the Tβ4+hydrocolloid dressing group (P＜0.05). However, there was no significant difference in the levels of TNF-α and IL-10 between the burn group and the p38MAPK agonist group at each time point (P＞0.05). Compared with the control group, the expressions of TGF-β1 mRNA and VEGF mRNA were all up-regulated at each time point in the burn group, Tβ4+ hydrocolloid dressing group and p38MAPK agonist group (P＜0.05). Compared with the burn group, the expression of TGF-β1 mRNA was down-regulated at each time point in the Tβ4+ hydrocolloid dressing group (P＜0.05), while the expression of VEGF mRNA was up-regulated (P＜0.05). There was no significant difference in the expressions of TGF-β1 mRNA and VEGF mRNA at each time point between the burn group and the p38MAPK agonist group (P＞0.05). Compared with the control group, the expression levels of p38MAPK, NF-κB and caspase-3 in the burn group, Tβ4+hydrocolloid dressing group and p38MAPK agonist group were all higher (P＜0.05); Compared with the burn group, the expression levels of p38MAPK, NF-κB and caspase-3 in the Tβ4+hydrocolloid dressing group were all lower (P＜0.05). However, there was no significant difference in the expression of p38MAPK, NF-κB and caspase-3 between the burn group and the p38MAPK agonist group (P＞0.05). 
Conclusion Adrenaline β4 combined with hydrocolloid dressing helps to promote the healing of deep Ⅱ degree burn wounds, and the mechanism may be related to the inhibition of p38 mitogen-activated protein kinase signal transduction pathway and the reduction of inflammatory factor expression. 

Key words: burns, thymosin β4, hydrocolloid dressing