A Toolbox to Investigate the Impact of Impaired Oxygen Delivery in Experimental Disease Models

Effects of remote ischemic preconditioning on early markers of intestinal injury in experimental hemorrhage in rats

The maintenance of intestinal integrity and barrier function under conditions of restricted oxygen availability is crucial to avoid bacterial translocation and local inflammation. Both lead to secondary diseases after hemorrhagic shock and might increase morbidity and mortality after surviving the initial event. Monitoring of the intestinal integrity especially in the early course of critical illness remains challenging. Since microcirculation and mitochondrial respiration are main components of the terminal stretch of tissue oxygenation, the evaluation of microcirculatory and mitochondrial variables could identify tissues at risk during hypoxic challenges, indicate an increase of intestinal injury, and improve our understanding of regional pathophysiology during acute hemorrhage. Furthermore, improving intestinal microcirculation or mitochondrial respiration, e.g. by remote ischemic preconditioning (RIPC) that was reported to exert a sufficient tissue protection in various tissues and was linked to mediators with vasoactive properties could maintain intestinal integrity. In this study, postcapillary oxygen saturation (µHbO2), microvascular flow index (MFI) and plasmatic D-lactate concentration revealed to be early markers of intestinal injury in a rodent model of experimental hemorrhagic shock. Mitochondrial function was not impaired in this experimental model of acute hemorrhage. Remote ischemic preconditioning (RIPC) failed to improve intestinal microcirculation and intestinal damage during hemorrhagic shock.

Local carbachol application induces oral microvascular recruitment and improves gastric tissue oxygenation during hemorrhagic shock in dogs

Introduction

Hemorrhagic shock is characterized by derangements of the gastrointestinal microcirculation. Topical therapy with nitroglycerine or iloprost improves gastric tissue oxygenation but not regional perfusion, probably due to precapillary adrenergic innervation. Therefore, this study was designed to investigate the local effect of the parasympathomimetic carbachol alone and in combination with either nitroglycerine or iloprost on gastric and oral microcirculation during hemorrhagic shock.

Methods

In a cross-over design five female foxhounds were repeatedly randomized into six experimental groups. Carbachol, or carbachol in combination with either nitroglycerine or iloprost were applied topically to the oral and gastric mucosa. Saline, nitroglycerine, or iloprost application alone served as control groups. Then, a fixed-volume hemorrhage was induced by arterial blood withdrawal followed by blood retransfusion after 1h of shock. Gastric and oral microcirculation was determined using reflectance spectrophotometry and laser Doppler flowmetry. Oral microcirculation was visualized with videomicroscopy. Statistics: 2-way-ANOVA for repeated measurements and Bonferroni post-hoc analysis (mean ± SEM; p < 0.05).

Results

The induction of hemorrhage led to a decrease of gastric and oral tissue oxygenation, that was ameliorated by local carbachol and nitroglycerine application at the gastric mucosa. The sole use of local iloprost did not improve gastric tissue oxygenation but could be supplemented by local carbachol treatment. Adding carbachol to nitroglycerine did not further increase gastric tissue oxygenation. Gastric microvascular blood flow remained unchanged in all experimental groups. Oral microvascular blood flow, microvascular flow index and total vessel density decreased during shock. Local carbachol supply improved oral vessel density during shock and oral microvascular flow index in the late course of hemorrhage.

Conclusion

The specific effect of shifting the autonomous balance by local carbachol treatment on microcirculatory variables varies between parts of the gastrointestinal tract. Contrary to our expectations, the improvement of gastric tissue oxygenation by local carbachol or nitroglycerine application was not related to increased microvascular perfusion. When carbachol is used in combination with local vasodilators, the additional effect on gastric tissue oxygenation depends on the specific drug combination. Therefore, modulation of tissue oxygen consumption, mitochondrial function or alterations in regional blood flow distribution should be investigated.

[Isodopharicin C inhibits NLRP3 inflammasome activation and alleviates septic shock in mice]

OBJECTIVE

To investigate the effect of Isodopharicin C (Iso C), a traditional Chinese herbal medicine extract, on NLRP3 inflammasome activation and lipopolysaccharide (LPS)-induced septic shock in mice.

METHODS

Murine bone marrow-derived macrophages (BMDM) and human monocytic THP-1 cells were stimulated with LPS before treatment with different NLRP3 inflammasome agonists to activate canonical NLRP3 inflammasomes. The non-canonical NLRP3 inflammasomes were activated by intracellular LPS transfection, and AIM2 inflammasomes were activated with poly A: T. The cleavage of caspase-1 induced by NLRP3 activation was measured using Western blotting. The levels of NLRP3-dependent and -independent pro-inflammatory cytokines in the cell culture supernatant were detected using ELISA, and the intracellular potassium ion concentration was measured using ICP-OES. In the animal experiment, C57BL/6J mouse models of septic shock (induced by intraperitoneal LPS injection) were treated with Iso C, and the levels of IL-1β, TNF-α and IL-6 in the serum and peritoneal lavage fluid were detected using ELISA. The survival time of the mice was observed within 48 h after LPS injection and a survival curve was plotted.

RESULTS

In BMDM cells, Iso C dose-dependently inhibited the activation of canonical NLRP3 inflammasomes and non-canonical NLRP3 inflammasomes (P<0.05) without obviously affecting the secretion levels of TNF-α and IL-6 (P>0.05), the activation of AIM2 inflammasomes (P>0.05), or K + efflux, the upstream signaling of NLRP3 activation (P>0.05). Iso C inhibited the activation of canonical NLRP3 inflammasomes in human THP-1 cells. In septic C57BL/6J mice, Iso C treatment significantly reduced IL-1β levels in the serum and peritoneal lavage fluid, and prolonged the survival time of the mice (P<0.05).

CONCLUSION

Iso C specifically inhibits NLRP3 inflammasome activation and alleviates septic shock in mice, and can serve as a potential small molecule compound for treatment of inflammatory diseases.