Sepsis induces platelet mitochondrial uncoupling and a gradual increase in respiratory capacity that is negatively associated with clinical outcome

Introduction

Mitochondrial dysfunction has been suggested as a contributing factor in the pathogenesis of multiple organ dysfunction syndrome (MODS) and sepsis is the leading cause of MODS. Also, restoration of mitochondrial function, known as mitochondrial biogenesis, has been implicated as a key factor for the recovery of organ function in patients with sepsis. Here we investigated platelet mitochondrial respiratory function in patients with sepsis during the first week after disease onset.

Methods

Platelets were isolated from blood samples taken from 18 patients with severe sepsis or septic shock within 48 hours of their admission to the intensive care unit. Subsequent samples were taken on days 3 to 4 and days 6 to 7. Eighteen healthy blood donors served as controls. Platelet mitochondrial function was determined by high-resolution respirometry. Endogenous respiration of intact platelets suspended in their own plasma or PBS glucose was determined and, in order to investigate the activity of individual complexes of the respiratory system, platelets were permeabilized with digitonin and stimulated with complex-specific substrates and inhibitors.

Results

There was a significant increase in maximal respiratory capacity of platelets from days 1 to 2 to days 6 to 7 as well as compared with controls in both intact platelets and permeabilized platelets oxidizing complex I and/or II linked substrates. Platelets suspended in their own septic plasma exhibited increased leak respiration compared with platelets suspended in PBS glucose and to controls. No inhibition of respiration was detected in septic patients compared with controls. Mortality at 90 days was 33% (6/18). Nonsurvivors had a significantly more elevated respiratory capacity at days 6 to 7 as compared with survivors. No correlation between respiratory capacity and severity of disease as measured by APACHE II, SAPS II, SOFA or noradrenaline dose were found. Platelet content of mitochondria-specific cytochrome c increased significantly, but no change in mitochondrial DNA was detected over the time interval studied.

Conclusions

The results indicate the presence of a soluble plasma factor in the initial stage of sepsis inducing uncoupling of platelet mitochondria but not inhibition of oxidative phosphorylation. Further, the mitochondrial uncoupling was paralleled by a gradual and substantial increase in respiratory capacity that may reflect mitochondrial biogenesis as a response to severe sepsis or septic shock. The enhanced respiratory capacity developing over the first week seems to reflect the severity of the condition and may be used as a prognostic marker of mortality.