[Effects of vitamin D₃ on intestinal mucosal barrier of mice with severe burns]

Objective: To explore the effects of vitamin D₃ on intestinal mucosal barrier of mice with severe burns. Methods: Forty-two C57BL/6C male mice aged eight to twelve weeks were divided into vitamin D₃ vehicle+ sham injury group of seven mice, vitamin D₃ vehicle+ burn injury group of fourteen mice, vitamin D₃+ sham injury group of seven mice, and vitamin D₃+ burn injury group of fourteen mice according to random number table. Mice in vitamin D₃ vehicle+ sham injury group and vitamin D₃ vehicle+ burn injury group were injected with vehicle of vitamin D₃ at a dose of 0.1 mL intraperitoneally at 1, 24, and 48 h before burn experiment. Mice in vitamin D₃+ sham injury group and vitamin D₃+ burn injury group were injected with vitamin D₃ at a dose of 100 ng/kg dissolved in 0.1 mL vehicle intraperitoneally at the same time points. Mice in vitamin D₃ vehicle+ burn injury group and vitamin D₃+ burn injury group were inflicted with 30% total body surface area full-thickness dermal scald (hereinafter referred to as burn) on the back by 98 ℃ hot water for 3 to 4 seconds. And mice in vitamin D₃ vehicle+ sham injury group and vitamin D₃+ sham injury were treated with 37 ℃ water on the back for 3 to 4 seconds to simulate injury. Seven mice in vitamin D₃ vehicle+ sham injury group and seven mice in vitamin D₃+ sham injury group at post injury hour (PIH) 24, and seven mice in vitamin D₃ vehicle+ burn injury group and seven mice in vitamin D₃+ burn injury group at PIH 6 and 24 were sacrificed respectively to collect mesentery lymph nodes, spleens, livers, and intestinal tissue. The mesentery lymph nodes, spleens, and livers of mice in each group were collected to observe growth of bacteria, and number of bacteria was counted. Intestinal tissue of mice in each group was collected to detect protein expressions of zonal occludin 1 (ZO-1) and occludin by immunohistochemistry staining method, distribution of ZO-1 by immunofluorescence staining method, and expression of occludin by Western blotting. Data were processed with Kruskal-Wallis H test, Nemenyi test, one-way analysis of variance, t test, and Bonferroni correction. Results: (1) At PIH 6 and 24, bacterial counts of mesentery lymph nodes, livers, and spleens of mice in vitamin D₃ vehicle+ burn injury group were significantly higher than those of mice in vitamin D₃ vehicle+ sham injury group (P<0.05). At PIH 6, bacterial counts of livers and spleens of mice in vitamin D₃+ burn injury group were significantly lower than those of mice in vitamin D₃ vehicle+ burn injury group (P<0.05). At PIH 24, bacterial counts of mesentery lymph nodes and livers of mice in vitamin D₃+ burn injury group were significantly lower than those of mice in vitamin D₃ vehicle+ burn injury group (P<0.05). (2) At PIH 6 and 24, expressions of ZO-1 and occludin of intestinal tissue of mice in vitamin D₃ vehicle+ burn injury group were significantly lower than those of mice in vitamin D₃ vehicle+ sham injury group, and expressions of ZO-1 and occludin of intestinal tissue of mice in vitamin D₃+ burn injury group were close to those of mice in vitamin D₃+ sham injury group. At PIH 6 and 24, expressions of ZO-1 and occludin of intestinal tissue of mice in vitamin D₃+ burn injury group were significantly higher than those of mice in vitamin D₃ vehicle+ burn injury group. (3) At PIH 6 and 24, compared with that of mice in vitamin D₃ vehicle+ sham injury group, distribution of ZO-1 of intestinal mucosal epithelium of mice in vitamin D₃ vehicle+ burn injury group was discontinuous. Distribution of ZO-1 of intestinal mucosal epithelium of mice in vitamin D₃+ sham injury group was normal, and the distribution of ZO-1 of intestinal mucosal epithelium of mice in vitamin D₃+ burn injury group was with good continuity. (4) At PIH 6 and 24, expressions of occludin of intestinal tissue of mice in vitamin D₃ vehicle+ burn injury group were 0.720±0.003, 0.638±0.052 respectively, significantly lower than 0.918±0.003 of mice in vitamin D₃ vehicle+ sham injury group (t=57.33, 5.36, P<0.05). At PIH 6 and 24, expressions of occludin of intestinal tissue of mice in vitamin D₃+ burn injury group were 0.994±0.058, 1.064±0.060, close to 0.938±0.023 of mice in vitamin D₃+ sham injury group (t=0.91, 1.96, P>0.05). At PIH 6 and 24, expressions of occludin of intestinal tissue of mice in vitamin D₃ vehicle+ burn injury group were significantly lower than those of mice in vitamin D₃+ burn injury group (t=4.75, 5.35, P<0.05). Conclusions: Intestinal bacterial translocation can occur in the early stage of severe burn. And vitamin D₃ plays a protective role in the intestinal mucosal barrier post severe burn to reduce the bacterial translocation by protecting tight junction proteins of intestinal epithelium.