Effect of early supplementation of exogenous carnitine on liver mitochondrial damage in severely scalded rats and its pathological mechanism

Objective To observe the effect of early supplementation of exogenous carnitine on liver mitochondrial damage in severely scalded rats and to explore its pathological mechanism. Methods Seventy-two adult female Sprague-Dawley rats were divided into sham injury group, scald injury group, and scald injury+ carnitine group according to the random number table, with 24 rats in each group. Rats in sham injury group was sham injured on the back by immersing in 37 ℃ water bath for 12 s without fluid replacement. While rats in scald injury and scald injury+ carnitine groups were inflicted with 30% total body surface area (TBSA) full-thickness scald on the back by immersing in 98 ℃water bath for 12 s. Immediately after injury, rats in scald injury group and scald injury+ carnitine group were injected with Ringer′s lactate solution with the dosage of 4 mL·kg^-1·%TBSA^-1 via tail vein according to the Parkland formula, meanwhile rats in scald injury+ carnitine group were injected with L-carnitine solution with dosage of 300 mg·kg^-1·d^-1 via tail vein from post injury hour (PIH) 1. At PIH 12, 24, 48 and 72, abdominal aorta blood and liver tissue were collected from 6 rats in each group. The serum levels of carnitine, β-hydroxybutyric acid, and ornithine carbamoyltransferase (OCT) were determined with enzyme-linked immuno sorbent assay, and the serum levels of lactate dehydrogenase (LDH), alanine aminotransferase(ALT), and aspartate transaminase (AST) was determined by automatic biochemical analyzer, Pathological changes of rats liver tissue were detected with HE staining. Data were processed with analysis of variance of factorial design and Student-Newman-Keulstest or Tamhane test, Bonferroni correction. Results (1) Compared with sham injury group, the serum level of carnitine of rats in scald injury group was significantly lower at each time point (P<0.05), and that of scald injury+ carnitine group was significantly lower at PIH 12, 24, and 48 (P<0.05). The serum level of carnitine of rats in scald injury+ carnitine group at PIH 72 [(28.2±3.0) μg/mL] was similar to that in sham injury group[(29.4±4.0) μg/mL, P>0.05]. The serum level of carnitine in scald injury+ carnitine group was significantly higher than that in scald injury group at each time point (P<0.05). (2) The serum levels of β-hydroxybutyric acid of rats in scald injury group and scald injury+ carnitine group were significantly lower than those in sham injury group at each time point (P<0.05). The serum levels of β-hydroxybutyric acid of rats in scald injury and scald injury+ carnitine groups both showed a trend of increase, and they peaked at PIH 72 [(1.77±0.30) , (2.93±0.44) mmol/L, respectively]. The serum levels of β-hydroxybutyric acid in scald injury+ carnitine group were significantly higher than those of scald injury group at each time point (P<0.05). (3) The serum levels of OCT of rats in scald injury and scald injury+ carnitine groups were significantly higher than those of sham injury group at each time point (P<0.05). The serum levels of OCT of rats in scald injury group and scald injury+ carnitine groups both showed a trend of decrease, and they peaked at PIH 12 [(186.28±6.77), (163.38±9.34) ng/mL, respectively]. The serum levels of OCT of rats in scald injury+ carnitine group were significantly lower than those of scald injury group at each time point (P<0.05). (4) Compared with those of sham injury group, the serum levels of LDH of rats in scald injury group were significantly higher at each time point (P<0.05). Compared with those of sham injury group, those of scald injury+ carnitine group were significantly higher at PIH 12 and 24 (P<0.05), which peaked at PIH 12 [(2 226±274) U/L]. The serum levels of LDH of rats in scald injury+ carnitine group were close to those of sham injury group at PIH 48 and72 (P>0.05). The serum levels of LDH of rats in scald injury+ carnitine group were significantly lower than those of scald injury group at each time point (P<0.05). (5) The serum levels of ALT and AST of rats in scald injury group and scald injury+ carnitine group were significantly higher than those of sham injury group at each time point (P<0.05). In scald injury+ carnitine group, the serum levels of ALT of rats were significantly lower than those in scald injury group at PIH 48 and 72 (P<0.05), and the serum level of AST of rats was significantly lower than that in scald injury group at PIH 48 (P<0.05), and the serum levels of AST and ALT of rats were close to those in scald injury group at other time points (P>0.05). The serum levels of ALT and AST in scald injury+ carnitine group both showed a trend of decrease, and they peaked at PIH 12 [(260±25), (1 511±145) U/L, respectively]. (6) The liver tissue of rats in sham injury group was basically normal at each time point. The degree of liver injury of rats in scald injury+ carnitine group was lighter than that in scald injury group. The liver tissue of rats in scald injury group at PIH 72 showed obvious cytoplasm loose, liver tissue structure loss with diffuse fatty degeneration and large coagulative necrosis. Only partially scattered fatty degeneration was observed in the liver tissue of ras in scald injury+ carnitine group. Conclusions By early supplementation of exogenous carnitine, serum levels of carnitine and β-hydroxybutyric acid can be restored to normal levels faster, alleviate mitochondrial damage of hepatocytes, and maintain the metabolic stability of hepatocytes in early stage of severe scald.