Noninvasive ventilation and high-flow nasal cannula (HFNC) are reasonable initial interventions reserving endotracheal intubation for worsening disease severity evidenced by increased work of ...breathing (WOB), risking respiratory muscle fatigue leading to hypoventilation, hypoxemia, and cardiac arrest and large transpulmonary pressure swings risking patient self-inflicted lung injury (SILI) 3, 4. Super-raters trained raters using a 4-min WOB scale video and tested their ability to correctly rate the WOB level in 80 non-intubated patients from the Emergency Department, medical wards, and the ICU with WOB ranging from 1 to 5. SEE PDF We examined the performance of our WOB scale in 10 patients admitted to the ICU with radiographic evidence of extensive COVID-19 pneumonia, significant hypoxemia, and multiple risk factors associated with poor outcome.
Several characteristics of the ventricular fibrillation (VF) waveform have been found predictive of successful defibrillation and hypothesized to reflect the myocardial energy state. In an open-chest ...swine model of VF, we modeled "average CPR" using extracorporeal circulation (ECC) and assessed the time course of coronary blood flow, myocardial metabolism, and myocardial structure in relation to the amplitude spectral area (AMSA) of the VF waveform without artifacts related to chest compression.
VF was induced and left untreated for 8 minutes in 16 swine. ECC was then started adjusting its flow to maintain a coronary perfusion pressure of 10 mmHg for 10 minutes. AMSA was calculated in the frequency domain and analyzed continuously with a 2.1 s timeframe and a Tukey window that moved ahead every 0.5 s.
AMSA progressively declined during untreated VF. With ECC, AMSA increased from 7.0 ± 1.9 mV·Hz (at minute 8) to 12.8 ± 3.3 mV·Hz (at minute 14) (p < 0.05) without subsequent increase and showing a modest correlation with coronary blood flow of borderline statistical significance (r = 0.489, p = 0.0547). Myocardial energy measurements showed marked reduction in phosphocreatine and moderate reduction in ATP with increases in ADP, AMP, and adenosine along with myocardial lactate, all indicative of ischemia. Yet, ischemia did not resolve during ECC despite a coronary blood flow of ~ 30% of baseline.
AMSA increased upon return of coronary blood flow during ECC. However, the maximal level was reached after ~ 6 minutes without further change. The significance of the findings for determining the optimal timing for delivering an electrical shock during resuscitation from VF remains to be further explored.
Out-of-hospital sudden cardiac arrest is a major public health problem with an overall survival of less than 5%. Upon cardiac arrest, cessation of coronary blood flow rapidly leads to intense ...myocardial ischemia and activation of the sarcolemmal Na
-H
exchanger isoform-1 (NHE-1). NHE-1 activation drives Na
into cardiomyocytes in exchange for H
with its exchange rate intensified upon reperfusion during the resuscitation effort. Na
accumulates in the cytosol driving Ca
entry through the Na
-Ca
exchanger, eventually causing cytosolic and mitochondrial Ca
overload and worsening myocardial injury by compromising mitochondrial bioenergetic function. We have reported clinically relevant myocardial effects elicited by NHE-1 inhibitors given during resuscitation in animal models of ventricular fibrillation (VF). These effects include: (a) preservation of left ventricular distensibility enabling hemodynamically more effective chest compressions, (b) return of cardiac activity with greater electrical stability reducing post-resuscitation episodes of VF, (c) less post-resuscitation myocardial dysfunction, and (d) attenuation of adverse myocardial effects of epinephrine; all contributing to improved survival in animal models. Mechanistically, NHE-1 inhibition reduces adverse effects stemming from Na
-driven cytosolic and mitochondrial Ca
overload. We believe the preclinical work herein discussed provides a persuasive rationale for examining the potential role of NHE-1 inhibitors for cardiac resuscitation in humans.
We have previously reported in HEK 293 T cells and in constitutive cyclophilin-D (Cyp-D) knockout (KO) mice that Cyp-D ablation downregulates oxygen consumption (VO
) and triggers an adaptive ...response that manifest in higher exercise endurance with less VO
. This adaptive response involves a metabolic switch toward preferential utilization of glucose
AMPK-TBC1D1 signaling nexus. We now investigated whether a similar response could be triggered in mice after acute ablation of Cyp-D using tamoxifen-induced ROSA26-Cre-mediated (i.e., conditional KO, CKO) by subjecting them to treadmill exercise involving five running sessions. At their first treadmill running session, CKO mice and controls had comparable VO
(208.4 ± 17.9 vs. 209.1 ± 16.8 ml/kg min
), VCO
(183.6 ± 17.2 vs. 184.8 ± 16.9 ml/kg min
), and RER (0.88 ± 0.043 vs. 0.88 ± 0.042). With subsequent sessions, CKO mice displayed more prominent reduction in VO
(genotype & session interaction
= 0.000) with less prominent reduction in VCO
resulting in significantly increased RER (genotype and session interaction
= 0.013). The increase in RER was consistent with preferential utilization of glucose as respiratory substrate (4.6 ± 0.8 vs. 4.0 ± 0.9 mg/min,
= 0.003). CKO mice also performed a significantly higher treadmill work for given VO
expressed as a power/VO
ratio (7.4 ± 0.2 × 10
vs. 6.7 ± 0.2 10
ratio,
= 0.025). Analysis of CKO skeletal muscle tissue after completion of five treadmill running sessions showed enhanced AMPK activation (0.669 ± 0.06 vs. 0.409 ± 0.11 pAMPK/β-tubulin ratio,
= 0.005) and TBC1D1 inactivation (0.877 ± 0.16 vs. 0.565 ± 0.09 pTBC1D1/β-tubulin ratio,
< 0.05) accompanied by increased glucose transporter-4 levels consistent with activation of the AMPK-TBC1D1 signaling nexus enabling increased glucose utilization. Taken together, our study demonstrates that like constitutive Cyp-D ablation, acute Cyp-D ablation also induces a state of increased O
utilization efficiency, paving the way for exploring the use of pharmacological approach to elicit the same response, which could be beneficial under O
limiting conditions.
ABSTRACT
Cyclophilin‐D (Cyp‐D) is a mitochondrial matrix peptidyl‐prolyl isomerase. Because cyclophilins can regulate nuclear gene expression, we examined whether Cyp‐D could regulate mitochondrial ...gene expression. We demonstrated in HEK 293T cells that transfected Cyp‐D interacts with mitochondrial transcription factors B1 and B2 (TFB2M) but not with mitochondrial transcription factor A. We also demonstrated that Cyp‐D interacts in vivo with TFB2M. Genetic silencing of Cyp‐D and pharmacologic inhibition of Cyp‐D markedly reduced mitochondrial transcription to 18 ± 5% (P < 0.05) and 24 ± 3% (P < 0.05) of respective controls. The level of interaction between Cyp‐D and TFB2M correlated with the level of nascent mitochondrial RNA intensity (r =0.896; P = 0.0156). Cyp‐D silencing down‐regulated mitochondrial transcripts initiated from the heavy strand promoter 2 i.e., NADH dehydrogenase 1 (ND1) by 11‐fold, P < 0.005; cytochrome oxidase 1 (COX1) by 4‐fold, P < 0.001; and ATP synthase subunit 6 (ATP6) by 6.5‐fold, P < 0.005); but not NADH dehydrogenase 6 (ND6), which is initiated from the light strand promoter. Cyp‐D silencing reduced mitochondrial membrane potential and cellular oxygen consumption (from 59 ± 5 to 34 ± 1 μmol oxygen/min/106 cells, P< 0.001); the latter without a statistically significant reversal after uncoupling electron transport from ATP synthesis, consistent with down‐regulation of electron transport complexes. Accordingly, these studies provide novel evidence that Cyp‐D could play a key role in regulating mitochondrial gene expression.— Radhakrishnan, J., Bazarek, S., Chandran, B., Gazmuri, R. J. Cyclophilin‐D: a resident regulator of mitochondrial gene expression. FASEB J. 29, 2734‐2748 (2015). www.fasebj.org
•Cyclophilin-D (Cyp-D) is a mitochondrial peptidyl-prolyl isomerase.•Cyp-D ablation in mice improves exercise capacity with less oxygen utilization.•Cyp-D ablation augments physical and ...cognitive-behavioral performance under hypoxic conditions.•Cyp-D modulation would be beneficial for oxygen limiting clinical conditions.
We recently reported that constitutive ablation of cyclophilin-D (Cyp-D) in mice reduces oxygen consumption (VO2) while paradoxically increasing exercise endurance, thereby demonstrating increased O2 utilization efficiency. This response was associated with augmented glucose uptake and glucose utilization, in part mediated through adenosine monophosphate-activated kinase signaling. We now hypothesized that Cyp-D knock-out (KO) mice might also exhibit improved cognitive-behavioral performance and that these favorable adaptive responses may persist under hypoxic conditions. We therefore assessed under normoxic (20.9% O2, simulating ground O2 levels) and hypoxic (8% O2, simulating 7600 m altitude O2 levels) conditions exercise capacity and cognitive-behavioral performance. We used a treadmill test to assess exercise capacity, a pole-test to assess agility, an elevated-plus-maze test to assess anti-anxiety, and a passive avoidance test to assess learning and memory retention. Compared to wild type, Cyp-D KO mice showed comparable treadmill work under normoxia (48 ± 12 vs 47 ± 9 Joules) but increased treadmill work (12 ± 1 vs 8 ± 1 Joules; p = 0.02) under hypoxia. Cyp-D KO mice displayed increased pole-descending time (17 ± 3 vs 8 ± 2 s; p ≤ 0.05) under normoxia but shorter pole-descending time (21 ± 3 vs 37 ± 4 s; p ≤ 0.01) under hypoxia. In addition, the Cyp-D KO mice demonstrated increased elevated plus-maze open arm time (91 ± 31 vs 23 ± 12 s; p ≤ 0.05) under hypoxia and increased latency to enter dark chamber (261 ± 23 vs 185 ± 42 s; p ≤ 0.05) under normoxia. Thus, our experiments showed that under normoxia Cyp-D KO mice displayed anti-anxiety behavior and improved learning and memory retention. Under hypoxia, Cyp-D KO mice displayed increased exercise capacity, increased agility, and increased anti-anxiety consistent with our previously reported findings of increased O2 utilization efficiency. Identifying interventions to elicit these effects could be beneficial in a myriad of physiological and clinical conditions in which increasing O2 utilization efficiency would be advantageous.
Reversal of cardiac arrest requires reestablishment of aerobic metabolism by reperfusion with oxygenated blood of tissues that have been ischemic for variable periods of time. However, reperfusion ...concomitantly activates a myriad of pathogenic mechanisms causing what is known as reperfusion injury. At the center of reperfusion injury are mitochondria, playing a critical role as effectors and targets of injury. Studies in animal models of ventricular fibrillation have shown that limiting myocardial cytosolic Na+ overload attenuates mitochondrial Ca2+ overload and maintains oxidative phosphorylation, which is the main bioenergetic function of mitochondria. This effect is associated with functional myocardial benefits such as preservation of myocardial compliance during chest compression and attenuation of myocardial dysfunction after return of spontaneous circulation. Additional studies in similar animal models of ventricular fibrillation have shown that mitochondrial injury leads to activation of the mitochondrial apoptotic pathway, characterized by the release of cytochrome c to the cytosol, reduction of caspase-9 levels, and activation of caspase-3 coincident with marked reduction in left ventricular function. Cytochrome c also "leaks" into the bloodstream attaining levels that are inversely proportional to survival. These data indicate that mitochondria play a key role during cardiac resuscitation by modulating energy metabolism and signaling apoptotic cascades and that targeting mitochondria could represent a promising strategy for cardiac resuscitation.
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