Membrane Permeant Inhibitor of Myosin Light Chain Kinase Worsens Survival in Murine Polymicrobial Sepsis

ABSTRACT

Sepsis-induced intestinal hyperpermeability is mediated by disruption of the epithelial tight junction, which is closely associated with the peri-junctional actin-myosin ring. Genetic deletion of myosin light chain kinase (MLCK) reverses intestinal hyperpermeability and improves survival in a murine model of intra-abdominal sepsis. In an attempt to determine whether these findings could be translated using a more clinically relevant strategy, this study aimed to determine if pharmacologic inhibition of MLCK using the membrane permeant inhibitor of MLCK (PIK) improved gut barrier function and survival following sepsis. C57BL/6 mice underwent cecal ligation and puncture to induce sepsis and were then randomized to receive either PIK or vehicle. Unexpectedly, PIK significantly worsened 7-day survival following sepsis (24% vs. 62%). The three pathways of intestinal permeability were then interrogated by orally gavaging septic mice with creatinine (6Å), FD-4 (28Å), and rhodamine70 (120Å) and assaying their appearance in the bloodstream. PIK led to increased permeability in the leak pathway with higher levels of FD-4 in the bloodstream compared to septic mice given vehicle. In contrast, no differences were detected in the pore or unrestricted pathways of permeability. Examination of jejunal tight junctions for potential mechanisms underlying increased leak permeability revealed that mice that received PIK had increased phosphorylated MLC without alterations in occludin, ZO-1, or JAM-A. PIK administration was not associated with significant differences in systemic or peritoneal bacterial burden, cytokines, splenic or Peyer's Patches immune cells or intestinal integrity. These results demonstrate that pharmacologic inhibition of MLCK unexpectedly increases mortality, associated with worsened intestinal permeability through the leak pathway, and suggest caution is required in targeting the gut barrier as a potential therapy in sepsis.

The microbiome and the immune system in critical illness

PURPOSE OF REVIEW

Although the gut microbiome plays a crucial role in the maintenance of health, it is hypothesized to drive morbidity and mortality in critically ill patients. This review describes the relationship between the gut microbiome and the immune system in critical illness.

RECENT FINDINGS

The gut microbiome is converted to a pathobiome in the ICU, characterized by decreased microbial diversity and pathogen predominance. These changes are induced by a pathologic microenvironment and are further exacerbated by common medical treatments initiated in the ICU. The conversion of the microbiome to a pathobiome has direct consequences on the regulation of inflammation and immunity by loss of beneficial host responses and initiation of maladaptive changes that can further propagate critical illness.

SUMMARY

The gut microbiome is dramatically altered in the ICU. In light of constant crosstalk between the microbiome and the host immune system, the pathobiome may play a key mechanistic role in driving a maladaptive response in critically ill patients. The pathobiome represents a potential therapeutic target in the management of critical illness whereby restoration of a healthier microbiome may directly alter the host inflammatory response, which could lead to improved patient outcomes.