New Insights into the Mechanisms of Vascular Dysfunction in a Young and Aged Septic Murine Model
Creators: Macala, Kimberly, F
Publisher: name: University of Alberta Library
Year: 2022

<p>Background:<br>
Sepsis is a dysregulated response to infection that results in life-threatening organ dysfunction. The elderly are disproportionately affected by sepsis and suffer an alarmingly high mortality rate. We hypothesized that increased mortality in the aged is due to a more highly dysfunctional vasculature secondary to loss of soluble guanylate cyclase signalling. As sepsis mortality is high, we aimed to provide insight into septic vascular dysfunction and discover a novel sepsis treatment that would be effective in the young and aged.</p>

<p>Methods:<br>
In all studies included herein, hemodynamics and vascular function were assessed in-vivo and ex-vivo.  In Study 1, young (3 to 4 months) and aged (22 to 24 months) mice were anesthetized and instrumented for hemodynamic assessments. Mice received an intraperitoneal injection of fecal slurry or an equivalent volume of vehicle. Systolic blood pressure, diastolic blood pressure, and heart rate were continuously recorded for a maximum of 600 minutes. A subset of mice received norepinephrine treatment. All mice received intravenous methacholine every 30 minutes to measure vascular reactivity. Following euthanization, tissues and arteries were collected for analysis of cGMP production and wire myography. Study 2 examined the young septic murine response to the soluble guanylate cyclase activator cinaciguat using the same protocol as above while Study 3 examined aged mice. The cytokine Oncostatin M is released in sepsis and plays a role in hemodynamic stability. As such, its receptor deficiency in both young males and females was investigated using a model of Oncostatin M receptor deficiency combined with the above septic protocol (Study 4).</p>

<p>Results: <br>
In study 1, aged mice had impaired non-septic and septic vasorelaxation responses in-vivo compared to the young. Non-septic aged mice were more responsive to methacholine, whereas septic aged mice were less responsive. Ultimately, aged mice demonstrated decreased sepsis survival. Conventional sepsis treatment with norepinephrine resulted in a similar sepsis survival time in both age groups. cGMP production in aged lung and kidney did not increase. Notable aged myography findings included increased sensitivity to methacholine in mesenteric arteries and increased vasorelaxation 120 minutes post-sepsis induction. </p>

<p>Due to the mortality associated with sepsis, we aimed to discover a treatment that would be effective in young (Study 2) and aged (Study 3) septic mice. Mice were treated with saline or the soluble guanylate cyclase activator cinaciguat to increase cGMP production and improve vascular dysfunction in sepsis. Cinaciguat improved the survival of young septic mice, coinciding with improved hemodynamics. Cinaciguat increased cGMP production in young lung and kidney. Myography revealed an increased sensitivity of cinaciguat-treated young septic mesenteric vessels to methacholine and sodium nitroprusside. Hemodynamic improvements were also noted in septic aged mice treated with cinaciguat. Baseline aged systolic and diastolic blood pressure response to methacholine was increased while septic blood pressure was decreased. Aged sepsis survival was also increased. However, no change in cGMP production was noted in aged lung or kidney. Myography demonstrated minimal vascular effect of cinaciguat. </p>

<p>In Study 4, both sexes of Oncostatin M receptor deficient mice displayed a distinct hemodynamic profile demonstrating systolic and diastolic hypertension as well as tachycardia. Septic response to methacholine was decreased in male but not female knockout mice (compared to controls). Oncostatin M deficiency did not improve survival for either sex. Oncostatin M receptor deficiency did demonstrate sex-specific myography effects associated with a decreased level of relaxation secondary to methacholine and sodium nitroprusside in both non-septic and septic male vessels. These changes were not seen in female vessels.</p>

<p>Summary and Conclusion:<br>
This is one of the first studies to examine both in-vivo and ex-vivo vascular function in a young and aged septic murine model. The findings demonstrate that aged septic mice experience vascular dysfunction, which may contribute to mortality. The novel use of cinaciguat resulted in augmentation of vascular function in young mice and improvement in sepsis survival in both young and aged mice. Finally, Oncostatin M receptor deficiency did not improve sepsis survival but led to the development of distinct non-septic and septic hemodynamic phenotypes.  Together, these results underscore the need to further delineate the mechanisms that underlie vascular dysfunction and septic circulatory collapse. This new information sets the stage for further testing of cinaciguat to understand the molecular mechanism(s) in improving septic outcomes.</p>