Cytokine and nitric oxide levels in patients with sepsis--temporal evolvement and relation to platelet mitochondrial respiratory function

Abstract

Background: The levels of nitric oxide (NO) and various cytokines are known to be increased during sepsis. These signaling molecules could potentially act as regulators and underlie the enhancement of mitochondrial function described in the later phase of sepsis. Therefore, we investigated the correlation between observed changes in platelet mitochondrial respiration and a set of pro- and anti-inflammatory cytokines as well as NO plasma levels in patients with sepsis.

Methods and results: Platelet mitochondrial respiration and levels of TNFα, MCP-1 (monocyte chemotactic protein-1), INFγ (interferon-γ), IL-1β, IL-4, IL-5, IL-6, IL-8, IL-10 and IL-17 and NO were analyzed in 38 patients with severe sepsis or septic shock at three time points during one week following admission to the ICU. Citrate synthase, mitochondrial DNA and cytochrome c were measured as markers of cellular mitochondrial content. All mitochondrial respiratory states increased over the week analyzed (p<0.001). IL-8 levels correlated with maximal mitochondrial respiration on day 6-7 (p = 0.02, r2 = 0.22) and was also higher in non-survivors compared to survivors on day 3-4 and day 6-7 (p = 0.03 respectively). Neither NO nor any of the other cytokines measured correlated with respiration or mortality. Cytochrome c levels were decreased at day 1-2 by 24±5% (p = 0.03) and returned towards values of the controls at the last two time points. Citrate synthase activity and mitochondrial DNA levels were similar to controls and remained constant throughout the week.

Conclusions: Out of ten analyzed cytokines and nitric oxide, IL-8 correlated with the observed increase in mitochondrial respiration. This suggests that cytokines as well as NO do not play a prominent role in the regulation of platelet mitochondrial respiration in sepsis. Further, the respiratory increase was not accompanied by an increase in markers of mitochondrial content, suggesting a possible role for post-translational enhancement of mitochondrial respiration rather than augmented mitochondrial mass.

Figure 1. Mitochondrial respiration.

Different respiratory states in controls and at three time points over one week in patients with sepsis in permeabilised (A) and intact cells incubated in their own plasma (B). Controls n = 38, patients n, 1st time point = 38, 2nd time point = 31, 3rd time point = 27. Displayed as mean ± SD. * = p<0.05, ** = p<0.01, *** = p<0.001.

Figure 2. Multiplex cytokines assay.

Plasma analysed from septic patients at three different time points (within 48 h, day 3–4 and day 6–7 of ICU stay). Controls were set to 100% for each cytokine and septic plasma values are expressed as log (%) relative difference. Controls n = 12, patients n, 1st time point = 38, 2nd time point = 31, 3rd time point  = 27, bars  =  median ± interquartile range. * = p<0.05, ** = p<0.01, *** = p<0.001 compared to controls.

Figure 3. Influence of septic plasma on mitochondrial respiration.

Intact platelets incubated for 1(white) or septic patients on day 1–2 (light grey), day 3–4 (dark grey) or day 6–7 (black) post admission to ICU. Stimulated to maximal respiration with FCCP. Controls n = 19, patients day 1–2 n = 18, day 3–4 and day 6–7 n = 17. Displayed as mean ± SD. * = p<0.05.