Prolonged Mechanical Ventilation Alters the Expression Pattern of Angio-neogenetic Factors in a Pre-Clinical Rat Model

Abstract

ObjectiveMechanical ventilation (MV) is a life saving intervention for patients with respiratory failure. Even after 6 hours of MV, diaphragm atrophy and dysfunction (collectively referred to as ventilator-induced diaphragmatic dysfunction, VIDD) occurs in concert with a blunted blood flow and oxygen delivery. The regulation of hypoxia sensitive factors (i.e. hypoxia inducible factor 1α, 2α (HIF-1α,–2α), vascular endothelial growth factor (VEGF)) and angio-neogenetic factors (angiopoietin 1–3, Ang) might contribute to reactive and compensatory alterations in diaphragm muscle.MethodsMale Wistar rats (n = 8) were ventilated for 24 hours or directly sacrificed (n = 8), diaphragm and mixed gastrocnemius muscle tissue was removed. Quantitative real time PCR and western blot analyses were performed to detect changes in angio-neogenetic factors and inflammatory markers. Tissues were stained using Isolectin (IB 4) to determine capillarity and calculate the capillary/fiber ratio.ResultsMV resulted in up-regulation of Ang 2 and HIF-1α mRNA in both diaphragm and gastrocnemius, while VEGF mRNA was down-regulated in both tissues. HIF-2α mRNA was reduced in both tissues, while GLUT 4 mRNA was increased in gastrocnemius and reduced in diaphragm samples. Protein levels of VEGF, HIF-1α, -2α and 4 did not change significantly. Additionally, inflammatory cytokine mRNA (Interleukin (IL)-6, IL-1β and TNF α) were elevated in diaphragm tissue.ConclusionThe results demonstrate that 24 hrs of MV and the associated limb disuse induce an up-regulation of angio-neogenetic factors that are connected to HIF-1α. Changes in HIF-1α expression may be due to several interactions occurring during MV.

Dysfunction of respiratory muscles in critically ill patients on the intensive care unit

“…Similar to patients with severe sepsis and septic shock, distinct cytokine cascades are upregulated. This includes interleukin (IL)‐6, tumour necrosis factor‐α, and IL‐1β in rat diaphragmatic tissue exposed to mechanical ventilation and may further amplify major inflammatory signalling pathways including NFkB . This ‘humoral’ response is well known to promote systemic immune cellular consequences and may also result in immune phenotypic changes .…”

“…It is therefore speculated that reduced oxygen delivery may lead to formation of reactive oxygen species with consecutive triggering of proteolytic cascades and enhanced oxidative stress . Angiogenetic factors change their expression profile under mechanical ventilation [downregulation of vascular endothelial growth factor (VEGF), upregulation of hypoxia‐inducible factor (HIF)‐1α], but their role in VIDD remains incompletely understood …”

“…This includes interleukin (IL)-6, tumour necrosis factor-α, and IL-1β in rat diaphragmatic tissue exposed to mechanical ventilation 47 and may further amplify major inflammatory signalling pathways including NFkB. 47,49 This 'humoral' response is well known to promote systemic immune cellular consequences and may also result in immune phenotypic changes. [50][51][52] There is experimental proof of diaphragmatic dysfunction directly induced by sepsis.…”

“…67 Angiogenetic factors change their expression profile under mechanical ventilation [downregulation of vascular endothelial growth factor (VEGF), upregulation of hypoxia-inducible factor (HIF)-1α], but their role in VIDD remains incompletely understood. 47,68 Exercise training or a genetically high aerobic capacity-interesting in the context of decreased blood supply-may protect the diaphragm from VIDD. Up-regulation of heat shock proteins and improved antioxidant properties of a 'trained diaphragm' with decreased activation of proteases and respective mitochondrial 'protection' are among the postulated mechanisms.…”

Kinetics of ventilation-induced changes in diaphragmatic metabolism by bilateral phrenic pacing in a piglet model

“…Therefore, unlike peripheral skeletal muscle that does not display hypoxia or a rapid reduction in blood flow and VO 2 with disuse, the diaphragm rapidly alters its metabolic rate (lower VO 2 ) with disuse, potentially as a result from the lowered perfusion. Indeed, we have observed an increased mRNA expression of HIF-1A in the diaphragm with prolonged CMV, suggesting a potential hypoxic microenvironment within the diaphragm 24 . The lactate/pyruvate ratio (LPR) has traditionally been used clinically to reflect potential tissue anaerobic metabolism.…”