Compartmentalization of lipid peroxidation in sepsis by multidrug-resistant gram-negative bacteria: experimental and clinical evidence

Abstract

Introduction: Recent evidence suggests a link between excess lipid peroxidation and specific organ failures in sepsis. No study has been performed in sepsis by multidrug-resistant (MDR) Gram-negative bacteria.

Methods: Lethal sepsis was induced in rats by the intraperitoneal injection of one MDR isolate of Pseudomonas aeruginosa. Produced malondialdehyde (MDA) was measured in tissues 5 hours after bacterial challenge with the thiobarbiturate assay followed by high-performance liquid chromatography (HPLC) analysis. Results were compared with those from a cohort of patients with ventilator-associated pneumonia (VAP) and sepsis by MDR Gram-negative bacteria. More precisely, serum MDA was measured on 7 consecutive days, and it was correlated with clinical characteristics.

Results: MDA of septic rats was greater in the liver, spleen, and aortic wall, and it was lower in the right kidney compared with sham operated-on animals. Findings were confirmed by the studied cohort. Circulating MDA was greater in patients with hepatic dysfunction and acute respiratory distress syndrome (ARDS) compared with patients without any organ failures. The opposite was found for patients with acute renal dysfunction. No differences were found between patients with ARDS without or with cardiovascular (CV) failure and patients without any organ failure. Serial measurements of MDA in serum of patients indicated that levels of MDA were greater in survivors of hepatic dysfunction and ARDS and lower in survivors of acute renal dysfunction.

Conclusions: Animal findings and results of human sepsis are complementary, and they suggest a compartmentalization of lipid peroxidation in systemic infections by MDR gram-negative bacteria.

Figure 1

Study flow chart. MDA, malondialdehyde; MDR, multidrug resistant; VAP, ventilator-associated pneumonia. The chest radiograph is of a patient enrolled in the study cohort, with permission.

Figure 2

Serial concentrations of tumor-necrosis factor-α (TNF-α) and malondialdehyde (MDA) after bacterial challenge. Experimental sepsis was induced in rats after the intraperitoneal injection of one multidrug-resistant isolate of Pseudomonas aeruginosa. At the indicated time intervals after challenge (n = 6 per time), rats were killed, and concentrations of MDA (a) and of TNF-α (b) were measured in serum. *P < 0.05 compared with the 5-hour interval after adjustment for multiple comparisons.

Figure 3

Tissue concentrations of MDA after bacterial challenge. Experimental sepsis was induced in rats after the intraperitoneal injection of 2 × 10⁷ cfu/animal of one multidrug-resistant isolate of Pseudomonas aeruginosa. Five hours after challenge (n = 6 per group), rats were killed, and concentrations of malondialdehyde (MDA) were measured in the tissue homogenates of liver (a), lung (b), spleen (c), right kidney (d), heart (e), and aorta (f). P values compared with sham-operated rats are shown.

Figure 4

Oxidative burst of circulating neutrophils. Experimental sepsis was induced in rats after the intraperitoneal injection of one multidrug-resistant isolate of Pseudomonas aeruginosa. Five hours after challenge (n = 6 per time), rats were killed, and oxidative burst on neutrophils was measured as the expression of dihydrorhodamine (DHR) on cell membranes after flow-cytometric analysis. P value compared with sham-operated rats is shown.

Figure 5

Serum concentrations of MDA in patients with sepsis. Concentrations of malondialdehyde (MDA) were measured on the first day of sepsis due to ventilator-associated pneumonia with multidrug-resistant gram-negative bacteria in 93 patients. Results are presented according to the types of failing organs: (a) patients with hepatic dysfunction versus patients without any organ failure; (b) patients with ARDS versus patients without any organ failure; (c) patients with ARDS and CV failure versus patients without any organ failure; (d) patients with CV failure without ARDS versus patients without any organ failure; and (e) patients with acute renal dysfunction versus patients without any organ failure). Circles denote outliers. P values reflect comparisons between patients without any organ failure and with the indicated organ failure. ARDS, acute respiratory distress syndrome; CV, cardiovascular.

Figure 6

Serum concentrations of MDA in patients with sepsis. Concentrations of malondialdehyde (MDA) were measured on the first day of sepsis due to ventilator-associated pneumonia with multidrug-resistant gram-negative bacteria in 93 patients. Results are presented according to the type of implicated pathogen. Circles denote outliers, and asterisks denote extremes.

Figure 7

Follow-up measurements of MDA of serum in patients with sepsis. Concentrations of malondialdehyde (MDA) were measured for 7 consecutive days in patients with ventilator-associated pneumonia with multidrug-resistant gram-negative bacteria and sepsis. Results are presented according to the type of failing organ: (a) patients with hepatic dysfunction; (b) only ARDS patients; (c) patients with ARDS and CV failure; (d) patients with CV failure without ARDS; and (e) patients with acute renal dysfunction, and separately for survivors (S) and nonsurvivors (NS). *P < 0.05 between S and NS.