Rapid changes in the microvascular circulation of skeletal muscle impair insulin delivery during sepsis

Abstract

IntroductionHyperglycemia is prevalent in hospitalized critically ill patients, even in those without a prior diagnosis of diabetes. In patients without pre‐existing diabetes, hyperglycemia is associated with increased morbidity and mortality. Hyperglycemia is one of the earliest clinical indications of sepsis, and clinical trials show that if the hyperglycemia is controlled, patient outcomes are improved. Previous investigations have focused on events in the myocyte (e.g. insulin signaling, glucose transport and subsequent metabolism) as the causes for this insulin resistant state. However, the delivery of insulin to the skeletal muscle (SkM) is an important determinant of insulin action.HypothesisReduced capillary blood flow to skeletal muscle belies the insulin resistance of sepsis by reducing insulin delivery to the myocyte and that protecting the endothelium from sepsis‐induced inflammation will prevent insulin resistance and reduced capillary blood flow.MethodIntravital microscopy was used to track fluorescent beads in mouse gastrocnemius muscle capillaries. Briefly, C57BL/6J mice with jugular vein catheters were anesthetized with isoflurane, and the gastrocnemius was exposed. Mice were then injected florescent beads. Images were subjected to a positional tracking. This data was used to build capillary flow speed maps for enhanced spatial visualization of flow data using MATLAB. Insulin delivery and insulin efflux out of the vessels were also examined using intravital microscopy and insulin conjugated with Alexa Flour 647.ResultsThis hypothesis was examined in mice treated with lipopolysaccharide (LPS) followed by intravital microscopy of the SkM microcirculation. We found that flowing capillary area was reduced by ~50% (Figure 1A) and velocity of blood flowing in the capillaries was slowed (Figure 1B) as well as more tortuous (Figure 1C) after LPS administration. We assessed capillary barrier permeability to insulin and surprisingly found no significant difference in insulin exchanges rates (iKT) for either control (0.25 Min−1) or LPS treated mice (0.21 Min−1). Next we determined insulin delivery to the SkM using two independent methods and found that sepsis rapidly reduces insulin delivery to the skeletal muscle by ~40%; this was driven by decreases in capillary flow velocity and number of perfused capillaries (Figure 2A&B). Further, the changes in SkM microcirculation occur prior to changes in both cardiac output and arterial blood pressure. Finally, we created mice with an endothelial specific knockdown of NFκB signaling through the deletion of P65 (P65eko) and found they were protected from both LPS‐induced reductions in blood flow speed and increases in blood flow tortuosity (Figure 2C).ConclusionThese data suggest that a rapid reduction in skeletal muscle insulin delivery contributes to the induction of insulin resistance during sepsis. Additionally, we determined that protecting the endothelium from inflammation prevents altered microvascular flow during sepsis.Support or Funding InformationR01 DK043748 DK078188 T32DK101003This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.