Microcirculatory-mitochondrial resuscitation with new anti-inflammatory therapies in experimental sepsis

Sepsis is a potentially life-threatening condition caused by a dysregulated host response to infection. Along with its progression, regulatory failure is frequently associated with a mismatch between oxygen delivery (DO2), oxygen consumption (VO2) and a deficit in oxygen extraction (ExO2) at the cellular level. The poorly functioning microvasculature reduces delivery of oxygen to the tissue, while the mitochondrial electron transport system (ETS) is deficient, being unable to use oxygen efficiently. These processes are closely linked and ultimately lead to microcirculatory and mitochondrial distress syndrome (MMDS), which is thought to mediate end organ damage. Given this background, the major goal of this thesis was to find a novel, clinically applicable maneuver for microcirculatory recruitment and mitochondrial resuscitation to minimize the energy deficit of the organs in experimental sepsis. In our studies Sprague Dawley rats were subjected to fecal peritonitis or a sham operation. Invasive monitoring and blood gas analysis were performed on anesthetized animals to evaluate organ dysfunctions together with intestinal capillary microperfusion and hepatic mitochondrial respiration. In Study 1, we characterized the time course of experimental sepsis-induced changes so as to determine the most relevant time points of data and sample collections and therapeutic interventions. In Study 2, we investigated the consequences of modulating the hypoxia-sensitive endothelin (ET) system, which plays an established role in circulatory regulation through vasoconstrictor ETA and ETB2 and vasodilator ETB1 receptors (ETA-R and ETB-R). Septic animals were treated with saline or ETA-R antagonist, ETB1-R agonist or a combination therapy 22 h after sepsis induction, while oxygen dynamics, mesenteric microcirculation and hepatic mitochondrial respiration were monitored. The ETB-R agonist countervailed the septic hypotension, while the ETA-R antagonist maintained microcirculation and oxygen dynamics. The combined treatment was able to integrate these beneficial effects. Study 3 focused on the effects of kynurenic acid (KYNA), a metabolite of the kynurenine pathway of tryptophan catabolism, which exhibits pleiotropic cell-protective effects under many inflammatory conditions. Septic animals were treated with saline or received KYNA or its synthetic analogue SZR-72 after 16 and 22 h of sepsis induction. It was found that treatment with SZR-72 directly modulates mitochondrial respiration, while administration of KYNA restores microcirculation. In conclusion, our results suggest that a mixed ET receptor-targeted treatment or therapy with KYNA or the synthetic analogue SZR-72 may offer novel possibilities for a simultaneous microcirculatory and mitochondrial resuscitation strategy in sepsis. Despite compartmentalization, the microcirculatory and mitochondrial functions are closely linked under physiological circumstances. The common denominator of both mechanisms may be the capillary-mitochondrial oxygen gradient, which may be a decisive factor in mitochondrial function in sepsis. Therefore, the efficacy of microcirculatory resuscitation therapies may also be manifested at the level of subcellular oxygen consumption and energy production, and these treatment strategies could provide a novel option via influencing septic microcirculatory and mitochondrial processes

Endothelin A and B receptors: potential targets for microcirculatory-mitochondrial therapy in experimental sepsis

The hypoxia-sensitive endothelin (ET) system plays an important role in circulatory regulation through vasoconstrictor ETA and ETB2 and vasodilator ETB1 receptors. Sepsis progression is associated with microcirculatory and mitochondrial disturbances along with tissue hypoxia. Our aim was to investigate the consequences of treatments with the ETA receptor (ETA-R) antagonist, ETB1 receptor (ETB1-R) agonist, or their combination on oxygen dynamics, mesenteric microcirculation and mitochondrial respiration in a rodent model of sepsis. Sprague Dawley rats were subjected to fecal peritonitis (0.6 g kg ip) or a sham operation. Septic animals were treated with saline or the ETA-R antagonist ETR-p1/fl peptide (100 nmol kg iv), the ETB1-R agonist IRL-1620 (0.55 nmol kg iv), or a combination therapy 22 h after induction. Invasive hemodynamic monitoring and blood gas analysis were performed during a 90-min observation, plasma ET-1 levels were determined, and intestinal capillary perfusion (CPR) was detected by intravital videomicroscopy. Mitochondrial Complex I (CI)- and CII-linked oxidative phosphorylation (OXPHOS) was evaluated by high-resolution respirometry in liver biopsies. Septic animals were hypotensive with elevated plasma ET-1. The ileal CPR, oxygen extraction (ExO2), and CI-CII-linked OXPHOS capacities decreased. ETR-p1/fl treatment increased ExO2 (by >45%), CPR, and CII-linked OXPHOS capacity. The administration of IRL-1620 countervailed the sepsis-induced hypotension (by >30%), normalized ExO2, and increased CPR. The combined ETA-R antagonist-ETB1-R agonist therapy reduced the plasma ET-1 level, significantly improved the intestinal microcirculation (by >41%), and reversed mitochondrial dysfunction. The additive effects of a combined ETA-R-ETB1-R-targeted therapy may offer a tool for a novel microcirculatory and mitochondrial resuscitation strategy in experimental sepsis