[Protective effect of insulin on burn serum-challenged cardiomyocytes in vitro]

To investigate the protective effect of insulin on burn serum-challenged cardiomyocytes in vitro.

Primary culture of cardiomyocytes from Sprague-Dawley (SD) 2-day-old neonate rats were divided into sham group, burn group, insulin group, and insulin activation inhibitor LY294002 pretreatment group (LY group). The model of cardiomyocytes injury induced by burn serum of 3-month-old SD rats [the serum of abdominal aortic was collected at 6 hours after modelling 30% total surface area (TBSA) III degree scald rat] was reproduced. In the insulin group, 10% burn serum and insulin (10 U/L) were added into cell culture medium, and in the LY group, LY294002 (50 μmol/L) was pretreated for 30 minutes before the addition of burn serum and insulin. Sham group was only given 10% serum of sham injured rats (sham rats were only placed in 37 centigrade warm water). After the cells were cultured for 12 hours, the release of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and creatine kinase (CK) were determined by enzyme-linked immunosorbent assay (ELISA). The cardiac troponin T (cTnT) protein expression was examined by Western Blot. Apoptosis of cardiomyocytes was observed after Hoechst 33258 staining.

Compared with the sham group, the cardiomyocytes were damaged and released inflammatory cytokines after burn serum-challenged. The levels of TNF-α, IL-6 and CK increased [TNF-α (ng/L): 273±48 vs. 21±6, IL-6 (ng/L): 416±83 vs. 44±11, CK (U/L): 1.44±0.24 vs. 0.14±0.08, all P < 0.01], while the expression of cTnT protein decreased (cTnT/β-actin: 0.12±0.04 vs. 0.86±0.34, P < 0.01), and the cardiomyocyte apoptosis increased [(19.1±5.6)% vs. (5.2±1.3)%, P < 0.01]. Insulin could significantly reduce the damage of cardiomyocytes, decrease the release of TNF-α, IL-6 and CK induced by burn serum [TNF-α (ng/L): 105±37 vs. 273±48, IL-6 (ng/L): 176±77 vs. 416±83, CK (U/L): 0.82±0.26 vs. 1.44±0.24, all P < 0.05], the expression of cTnT protein significantly increased (cTnT/β-actin: 0.41±0.16 vs. 0.12±0.04, P < 0.05), and the cells apoptosis rate significantly decreased [(10.7±3.2)% vs. (19.1±5.6)%, P < 0.05]. Further blocking experiments showed that LY294002 could mitigate the protective effects of insulin.

For cardiomyocytes challenged by burn serum, insulin may decrease inflammation, apoptosis and then protect the cardiomyocytes.