Hyperglycemia in a rat CLP model of sepsis is associated with mitochondrial uncoupling

Background

Tight glucose control was shown to greatly improve the morbidity and mortality of septic ICU patients [1]. The mechanism by which hyperglycemia is detrimental is not clearly understood.

Hypothesis

Hyperglycemia is associated with hepatic dysfunction of the mitochondrial respiratory chain (MRC).

Methods

Male Sprague-Dawley rats, 250–400 g, were used. We followed glucose levels in rats made septic by cecal ligation and perforation (CLP) over time (tail puncturing). We also evaluated MRC in isolated liver mitochondria at different time-points post-CLP. Enzymatic activities of MRC complexes I-IV were measured by spectrophotometry and respiration was measured by an oxygen electrode with glutamate + malate as substrates. The respiratory control ratio (RCR), calculated as the ratio of oxygen uptake in the presence and absence of ADP, served as an indicator for coupling. Sham laparotomy rats served as controls.

Results

Hyperglycemia was evident 6 hours post-CLP, followed by a significant decrease of the blood glucose level (Fig. 1). Mitochondrial dysfunction was manifested as an up to 48% reduction of the RCR (Fig. 2). A mild reduction of oxygen consumption and MRC complexes I, II and IV (70%, 77%, 57% and 73% residual activity respectively, compared with controls) was observed at 6 hours post-CLP.

Figure 1

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Figure 2

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Conclusion

This rat CLP model of sepsis, in its early hours, mimics human septic hyperglycemia. Impaired function of a septic rat's liver mitochondria (markedly decreased coupling and moderately decreased MRC activities) is evident following the time-period of hyperglycemia in this model.