Patricia A.C. Specht

Ventilator-induced endothelial activation and inflammation in the lung and distal organs

IntroductionResults from clinical studies have provided evidence for the importance of leukocyte-endothelial interactions in the pathogenesis of pulmonary diseases such as acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), as well as in systemic events like sepsis and multiple organ failure (MOF). The present study was designed to investigate whether alveolar stretch due to mechanical ventilation (MV) may evoke endothelial activation and inflammation in healthy mice, not only in the lung but also in organs distal to the lung.MethodsHealthy male C3H/HeN mice were anesthetized, tracheotomized and mechanically ventilated for either 1, 2 or 4 hours. To study the effects of alveolar stretch in vivo, we applied a MV strategy that causes overstretch of pulmonary tissue i.e. 20 cmH2O peak inspiratory pressure (PIP) and 0 cmH20 positive end expiratory pressure (PEEP). Non-ventilated, sham-operated animals served as a reference group (non-ventilated controls, NVC).ResultsAlveolar stretch imposed by MV did not only induce de novo synthesis of adhesion molecules in the lung but also in organs distal to the lung, like liver and kidney. No activation was observed in the brain. In addition, we demonstrated elevated cytokine and chemokine expression in pulmonary, hepatic and renal tissue after MV which was accompanied by enhanced recruitment of granulocytes to these organs.ConclusionsOur data implicate that MV causes endothelial activation and inflammation in mice without pre-existing pulmonary injury, both in the lung and distal organs.

Acute respiratory distress syndrome leads to reduced ratio of ACE/ACE2 activities and is prevented by angiotensin‐(1–7) or an angiotensin II receptor antagonist

Acute respiratory distress syndrome (ARDS) is a devastating clinical syndrome. Angiotensin‐converting enzyme (ACE) and its effector peptide angiotensin (Ang) II have been implicated in the pathogenesis of ARDS. A counter‐regulatory enzyme of ACE, ie ACE2 that degrades Ang II to Ang‐(1–7), offers a promising novel treatment modality for this syndrome. As the involvement of ACE and ACE2 in ARDS is still unclear, this study investigated the role of these two enzymes in an animal model of ARDS. ARDS was induced in rats by intratracheal administration of LPS followed by mechanical ventilation. During ventilation, animals were treated with saline (placebo), losartan (Ang II receptor antagonist), or with a protease‐resistant, cyclic form of Ang‐(1–7) [cAng‐(1–7)]. In bronchoalveolar lavage fluid (BALF) of ventilated LPS‐exposed animals, ACE activity was enhanced, whereas ACE2 activity was reduced. This was matched by enhanced BALF levels of Ang II and reduced levels of Ang‐(1–7). Therapeutic intervention with cAng‐(1–7) attenuated the inflammatory mediator response, markedly decreased lung injury scores, and improved lung function, as evidenced by increased oxygenation. These data indicate that ARDS develops, in part, due to reduced pulmonary levels of Ang‐(1–7) and that repletion of this peptide halts the development of ARDS. Copyright

Ventilator-Induced Inflammatory Response in Lipopolysaccharide-Exposed Rat Lung Is Mediated by Angiotensin-Converting Enzyme

Angiotensin-converting enzyme (ACE) mediates the ventilator-induced inflammatory response in healthy lungs via angiotensin II (Ang II). A rat model was used to examine the role of ACE and Ang II in the inflammatory response during mechanical ventilation of preinjured (ie, lipopolysaccharide [LPS]-exposed) lungs. When indicated, rats were pretreated with the ACE inhibitor captopril and/or intratracheal administration of LPS. The animals were ventilated for 4 hours with moderate pressure amplitudes. Nonventilated animals served as controls. ACE activity and levels of Ang II and inflammatory mediators (interleukin-6, Cytokine-induced Neutrophil Chemoattractant (CINC)-3, interleukin-1beta, and interleukin-10) were determined in bronchoalveolar lavage fluid (BALF). The localization of ACE and Ang II type 1 receptor in lung tissue was determined by immunohistochemistry. The role of the Ang II pathway was assessed by using its receptor antagonist Losartan. Mechanical ventilation of LPS-exposed animals increased ACE activity and levels of inflammatory mediators in BALF compared with ventilated nonexposed and LPS-exposed nonventilated animals. Blocking ACE by captopril attenuated the lung inflammatory response. Furthermore, increased ACE activity in BALF was accompanied by increased levels of Ang II and enhanced expression of its receptor on alveolar cells. Blocking the Ang II receptor attenuated the inflammatory mediator response to a larger extent than by blocking ACE. In conclusion, during mechanical ventilation ACE, via Ang II, mediates the inflammatory response of both healthy and preinjured lungs.

Renal damage susceptibility and autoregulation in RF-1 and RF-5 congenic rats.

Background:Linkage analyses of crosses of rats susceptible to renal damage, fawn-hooded hypertensive (FHH), and those resistant to kidney damage, August × Copenhagen Irish (ACI), indicated that five quantitative trait loci (QTLs), Rf-1 to Rf-5, influence proteinuria (UPV), albuminuria (UAV) and focal glomerulosclerosis (FGS). Here we present data obtained in congenic rats to directly assess the role of the Rf-1 and Rf-5 QTLs. Methods:Renal damage (UPV, UAV, and FGS) was assessed in ACI, ACI.FHH-(D1Rat324-D1Rat156)(Rf-1B), and ACI.FHH-(D17Rat117-D17Arb5)(D17Rat180-D17Rat51) (Rf-5) congenic rats in the two-kidney (2K) control situation, and following L-NAME-induced hypertension, unilateral nephrectomy (UNX), and UNX combined with L-NAME. In addition we investigated renal blood flow (RBF) autoregulation in 2K congenic and parental ACI and FHH rats. Results:Compared to ACI, Rf-1B congenic rats showed a significant increase in susceptibility to renal damage after all three treatments. The increase was most pronounced after UNX with L-NAME. In contrast, the degree of renal damage in Rf-5 congenic rats was not different from the ACI. Like FHH, Rf-1B rats had impaired renal autoregulation. In contrast, RBF autoregulation of Rf-5 rats does not differ from ACI. Conclusion:The Rf-5 QTL does not show any direct effect. The Rf-1 QTL carries one or more genes impairing renal autoregulation and influencing renal damage susceptibility. Whether these are the same genes remains to be established.

The effects of intravenous nitroglycerine and norepinephrine on gastric microvascular perfusion in an experimental model of gastric tube reconstruction

BACKGROUND Esophagectomy with gastric tube reconstruction is the surgical treatment for cancer of the esophagus. Perfusion of the anastomotic site of the tube depends exclusively on microcirculation, making it susceptible to hypoperfusion. It is unknown whether vasodilatation is superior to increased perfusion pressure to improve gastric tissue perfusion of the anastomosis. METHODS We performed a gastric tube reconstruction in 12 pigs, mean body weight 32 +/- 2 kg. Besides systemic hemodynamic parameters, gastric microvascular blood flow (MBF) was assessed with laser Doppler flowmetry and gastric microvascular HbO(2) saturation (microHbSO(2)) and Hb concentration (microHbcon) with spectrophotometry. Animals were randomized over 2 groups: with and without intravenous nitroglycerin (NTG). In both groups, mean arterial pressure (MAP) was increased from 50 to 110 mmHg with infusion of norepinephrine; in the NTG group, central venous pressure was maintained below 10 mmHg throughout the experiment with NTG. RESULTS Except for central venous and pulmonary capillary wedge pressures, all hemodynamic parameters were similar in both groups. Especially in corpus and fundus, MBF decreased following surgery. However, overall MBF was significantly higher in the NTG group. Increasing MAP had no effect on fundus MBF. Gastric microHbSO(2) and microHbcon were not different between groups and did not change at higher MAP levels. CONCLUSION In our experimental model of gastric tube reconstruction, tissue perfusion is severely compromised; this effect is aggravated by systemic hypotension independent from cardiac output. Impaired venous outflow might contribute to this effect and can be counteracted with infusion of nitroglycerine.

Absence of an interaction between the Rf-1 and Rf-5 QTLs influencing susceptibility to renal damage in rats.

Background: Previous studies showed that combining the Rf-1 and Rf-3 or Rf-4 QTLs of FHH induced synergistic interactions markedly enhancing renal susceptibility. The present study aimed to determine the presence of such interaction between the Rf-1 and Rf-5 QTLs. Methods: Renal damage susceptibility was assessed in Rf-1B, Rf-1B+5, Rf-1B+4 congenics and ACI control rats in four situations: two-kidney control (2K), unilateral nephrectomy (UNX), L-NAME-induced hypertension (2K+L-NAME) and UNX+L-NAME. Albuminuria (UAV) and systolic blood pressure (SBP) were measured during 18 weeks of follow-up. In separate experiments, renal autoregulation was assessed in 2K rats. Results: In all four situations, Rf-1B+4 rats developed more severe UAV than ACI, Rf-1B and Rf-1B+5. There were no significant differences in UAV between Rf-1B and Rf-1B+5 rats. In the 2K and UNX situation no differences in SBP were noted between all four strains. With 2K+L-NAME and UNX+L-NAME treatment, SBP in double congenics was higher than that of ACI and Rf-1B rats. Renal autoregulation was similarly impaired in all three congenic strains. Conclusion: We conclude that the Rf-5 region, alone or in the presence of Rf-1B, does not affect the development of renal damage. We cannot substantiate that the Rf-5 region contains genes influencing renal damage susceptibility.

Oxygenation measurement by multi-wavelength oxygen-dependent phosphorescence and delayed fluorescence: catchment depth and application in intact heart

Oxygen delivery and metabolism represent key factors for organ function in health and disease. We describe the optical key characteristics of a technique to comprehensively measure oxygen tension (PO(2)) in myocardium, using oxygen-dependent quenching of phosphorescence and delayed fluorescence of porphyrins, by means of Monte Carlo simulations and ex vivo experiments. Oxyphor G2 (microvascular PO(2)) was excited at 442 nm and 632 nm and protoporphyrin IX (mitochondrial PO(2)) at 510 nm. This resulted in catchment depths of 161 (86) µm, 350 (307) µm and 262 (255) µm respectively, as estimated by Monte Carlo simulations and ex vivo experiments (brackets). The feasibility to detect changes in oxygenation within separate anatomical compartments is demonstrated in rat heart in vivo. Schematic of ex vivo measurements.

Feasibility of in vivo contrast-enhanced imaging of the renal cortex during hemorrhagic shock

A direct and non-invasive measurement of kidney function could aid in early recognition of acute kidney injury (AKI) at bedside and may prevent severe kidney damage. This study investigates the feasibility of contrast-enhanced ultrasound (CEUS) imaging of the renal cortex in an in vivo pig model of hemorrhagic shock. We hypothesize that the inflow-slope (SL) of the time-intensity curves (TICs) is lower as a result of decreased renal blood flow (RBF) in shock, caused by severe hemorrhage. Sixteen pigs underwent surgery to expose the right kidney and hemorrhagic shock was induced. Hemodynamics were measured at baseline (t0), 15 min after blood withdrawal (t1: early shock), and 60 min later (t2: late shock). RBF was measured using an ultrasonic flow probe, which was considered as the golden standard for measuring flow. For the CEUS measurements a bolus of microbubbles was injected in the jugular vein and imaged using the Vevo2100 (VisualSonics) transmitting at 18 MHz and recording 10 frames per second. Regions of interest were drawn in the cortex and TICs were analyzed. We showed that changes in the renal cortical inflow slope could be measured using CEUS. However, our results indicate a disparity in the kidney in response to hemorrhagic shock: a decrease in RBF results in an increase of microbubble-inflow in the renal cortex. As the flow probe placed around the renal artery measured flow of red blood cells, we can conclude that the inflow-slope of the TIC does not directly reflect the flow of red blood cells.