Andrea Olschewski

Pulmonary vascular resistances during exercise in normal subjects: a systematic review

The physiological range of pulmonary vascular resistance (PVR) and total pulmonary resistance (TPR), and the impact of exercise, age and posture have been a matter of debate for many years. We performed a systematic literature review including all right heart catheterisation data where individual PVR and TPR of healthy subjects both at rest and exercise were available. Data were stratified according to age, exercise level and posture. Supine resting PVR in subjects aged <24 yrs, 24–50 yrs, 51–69 yrs and ≥70 yrs was 61±23, 69±28, 86±15 and 90±39 dyn·s·cm−5, respectively. Corresponding TPR was 165±50, 164±46, 226±64 and 223±45 dyn·s·cm−5, respectively. During moderate exercise in subjects aged ≤50 yrs, an 85% increase in cardiac output was associated with a 25% decrease in TPR (p<0.0001) and a 12% decrease in PVR (p<0.01). At 51–69 yrs of age there was no significant decrease in TPR and PVR. In individuals aged ≥70 yrs TPR even increased by 17% (p=0.01), while PVR did not change significantly. At higher exercise levels, TPR decreased in all age groups. In the upright position, based on a limited number of data, resting TPR and PVR were higher than in the supine position and decreased more prominently during exercise, suggesting the release of resting pulmonary vasoconstriction. These data may form a basis to define normal PVR at rest and exercise.

PCK2 activation mediates an adaptive response to glucose depletion in lung cancer

Cancer cells are reprogrammed to utilize glycolysis at high rates, which provides metabolic precursors for cell growth. Consequently, glucose levels may decrease substantially in underperfused tumor areas. Gluconeogenesis results in the generation of glucose from smaller carbon substrates such as lactate and amino acids. The key gluconeogenic enzyme, phosphoenolpyruvate carboxykinase (PEPCK), has been shown to provide metabolites for cell growth. Still, the role of gluconeogenesis in cancer is unknown. Here we show that the mitochondrial isoform of PEPCK (PCK2) is expressed and active in three lung cancer cell lines and in non-small cell lung cancer samples. PCK2 expression and activity were enhanced under low-glucose conditions. PEPCK activity was elevated threefold in lung cancer samples over normal lungs. To track the conversion of metabolites along the gluconeogenesis pathway, lung cancer cell lines were incubated with 13C3-lactate and label enrichment in the phosphoenolpyruvate (PEP) pool was measured. Under low glucose, all three carbons from 13C3-lactate appeared in the PEP pool, further supporting a conversion of lactate to pyruvate, via pyruvate carboxylase to oxaloacetate, and via PCK2 to phosphoenolpyruvate. PCK2 small interfering RNA and the pharmacological PEPCK inhibitor 3-mercaptopicolinate significantly enhanced glucose depletion-induced apoptosis in A549 and H23 cells, but not in H1299 cells. The growth of H23 multicellular spheroids was significantly reduced by 3-mercaptopicolinate. The results of this study suggest that lung cancer cells may utilize at least some steps of gluconeogenesis to overcome the detrimental metabolic situation during glucose deprivation and that in human lung cancers this pathway is activated in vivo.

ATP-Dependent Potassium Channel in Rat Cardiomyocytes Is Blocked by Lidocaine Possible Impact on the Antiarrhythmic Action of Lidocaine

BACKGROUND During myocardial ischemia, lidocaine has favorable antiarrhythmic properties. Malignant arrhythmias result from heterogeneity between ischemic and nonischemic regions in extracellular potassium concentration and action potential duration. These effects have been attributed to the activation of ATP-dependent potassium (KATP) channels. In this study, we investigated the action of lidocaine on the KATP channels to test the possible link between the antiarrhythmic properties of lidocaine and its action on the KATP channel. METHODS AND RESULTS The patch-clamp technique was employed on enzymatic dissociated cardiomyocytes of adult rats. Lidocaine was applied to the outer side of excised membrane patches by means of a multibarrel perfusion system. Lidocaine reversibly blocked the mean current of the KATP channels in a concentration-dependent manner (IC50 = 43 +/- 4.7 mumol/L, E = 0 mV, n = 6), while the amplitude of the single-channel current remained unchanged. The half-maximum blocking concentration corresponds to the therapeutic range for the antiarrhythmic application of a lidocaine bolus in humans. CONCLUSIONS The open probability but not the conductance of the KATP channel in the membrane of rat cardiomyocytes is blocked by lidocaine. This action may explain, in part, the favorable antiarrhythmic properties of lidocaine during acute myocardial ischemia.

Local anaesthetics block hyperpolarization-activated inward current in rat small dorsal root ganglion neurones.

Hyperpolarizing voltage steps evoke slowly activating inward currents in a variety of neurones and in cardiac cells. This hyperpolarization‐activated inward current (Ih) is thought to play a significant role in cell excitability, firing frequency, or in setting of the resting membrane potential in these cells. We studied the effects of lidocaine, mepivacaine, QX‐314 and bupivacaine as well as its enantiomers on Ih in the membrane of dorsal root ganglion neurones (DRG). The patch‐clamp technique was applied to small dorsal root ganglion neurones identified in 200 μM thin slices of young rat DRGs. Under voltage‐clamp conditions, the whole‐cell Ih current was recorded in the presence of different concentrations of the local anaesthetics. In current‐clamp mode the resting membrane potential and the voltage response of DRG neurones to injected current pulses were investigated. Ih was reversibly blocked by bupivacaine, lidocaine and mepivacaine applied externally in clinically relevant concentrations. Concentration–response curves gave half‐maximum inhibiting concentrations of 55, 99 and 190 μM, respectively. Bupivacaine block of the Ih current was not stereoselective. No significant effect was observed when QX‐314 was applied to the external surface of the membrane. In current‐clamp experiments 60 μM bupivacaine slightly hyperpolarized the membrane. The membrane stimulation by low‐amplitude current pulses in the presence of bupivacaine showed an increase of the hyperpolarizing responses. Our findings suggest an important role of the Ih‐block by local anaesthetics in the complex mechanism of drug action during epidural and spinal anaesthesia.

Enhancement of delayed-rectifier potassium conductance by low concentrations of local anaesthetics in spinal sensory neurones

Combining the patch‐clamp recordings in slice preparation with the ‘entire soma isolation’ method we studied action of several local anaesthetics on delayed‐rectifier K+ currents in spinal dorsal horn neurones. Bupivacaine, lidocaine and mepivacaine at low concentrations (1–100 μM) enhanced delayed‐rectifier K+ current in intact neurones within the spinal cord slice, while exhibiting a partial blocking effect at higher concentrations (>100 μM). In isolated somata 0.1–10 μM bupivacaine enhanced delayed‐rectifier K+ current by shifting its steady‐state activation characteristic and the voltage‐dependence of the activation time constant to more negative potentials by 10–20 mV. Detailed analysis has revealed that bupivacaine also increased the maximum delayed‐rectifier K+ conductance by changing the open probability, rather than the unitary conductance, of the channel. It is concluded that local anaesthetics show a dual effect on delayed‐rectifier K+ currents by potentiating them at low concentrations and partially suppressing at high concentrations. The phenomenon observed demonstrated the complex action of local anaesthetics during spinal and epidural anaesthesia, which is not restricted to a suppression of Na+ conductance only.

Mild Elevation of Pulmonary Arterial Pressure as a Predictor of Mortality

Rationale: Normal mean pulmonary arterial pressure (mPAP) is 14.0 ± 3.3 mm Hg (mean ± SD). The prognostic relevance of mildly elevated mPAP not fulfilling the definition of pulmonary hypertension (PH; mPAP ≥ 25 mm Hg) has not been prospectively evaluated in a real‐world setting. Objectives: To assess the association of resting mPAP with all‐cause mortality in a retrospective and a prospective cohort of patients with unexplained dyspnea and/or at risk of PH. Methods: Prognostic cutoffs were calculated by means of 1) classification and regression tree (CART) analysis without any preset thresholds, and 2) preset thresholds on the basis of literature data defining mPAP as lower‐normal (≤mean + 1 SD), upper‐normal (between mean + 1 SD and mean + 2 SD), borderline (between mean + 2 SD and 25 mm Hg), and manifest PH (≥25 mm Hg). We performed univariate and multivariate survival analysis adjusted for age and comorbidities. Measurements and Main Results: We enrolled 547 patients, of whom 137, 56, 64, and 290 presented with lower‐normal, upper‐normal, or borderline mPAP, and manifest PH, respectively. The CART analysis on mPAP discriminated three prognostic groups: mPAP less than 17 mm Hg, 17 to 26 mm Hg, and greater than 26 mm Hg, with significantly decreasing survival. The univariate analysis on the basis of preset thresholds showed that upper‐normal mPAP, borderline mPAP, and manifest PH were significantly associated with poor survival compared with lower‐normal mPAP. In the multivariate model, considering age and comorbidities, only borderline mPAP (hazard ratio, 2.37; 95% confidence interval, 1.14‐4.97; P = 0.022) and manifest PH (hazard ratio, 5.05; 95% confidence interval, 2.79‐9.12; P < 0.001) were significantly associated with poor survival. Conclusions: In patients at risk for PH and/or with unexplained dyspnea, CART analysis detects prognostic thresholds at a resting mPAP of 17 mm Hg and 26 mm Hg, and values between 20 mm Hg and 25 mm Hg represent an independent predictor of poor survival. Clinical trial registered with www.clinicaltrials.gov (NCT 01607502).

A pro-con debate: current controversies in PAH pathogenesis at the American Thoracic Society International Conference in 2017

The following review summarizes the pro-con debate about current controversies regarding the pathogenesis of pulmonary arterial hypertension (PAH) that took place at the American Thoracic Society Conference in May 2017. Leaders in the field of PAH research discussed the importance of the immune system, the role of hemodynamic stress and endothelial apoptosis, as well as bone morphogenetic protein receptor-2 signaling in PAH pathogenesis. Whereas this summary does not intend to resolve obvious conflicts in opinion, we hope that the presented arguments entice further discussions and draw a new generation of enthusiastic researchers into this vibrant field of science to bridge existing gaps for a better understanding and therapy of this fatal disease.

Redox Signaling in Hypoxic Pulmonary Vasoconstriction

Changes in oxygen tension are sensed by a variety of tissues, such as the carotid body, ductus arteriosus (DA), and pulmonary vasculature. In the fetus, hypoxia keeps the DA open and the pulmonary vessels constricted. After birth, hypoxic pulmonary vasoconstriction (HPV) helps to match ventilation and perfusion. HPV is induced by three general mechanisms—influx of calcium into the smooth muscle cells through L-type channels and store-operated channels, release of calcium from the sarcoplasmic reticulum, and sensitization of actin/myosin to a given level of calcium. We show that reducing agents mimic the effects of hypoxia by reducing potassium current, causing membrane depolarization and increasing calcium influx in pulmonary artery smooth muscle cells (PASMCs), while doing exactly the opposite in the DA. On the other hand, oxidizing agents mimic normoxia by increasing potassium current, causing membrane hyperpolarization and reducing cytosolic calcium in PASMCs. They again do the opposite in the DA. As these redox agents elicit the same responses as shifts in oxygen tension, we consider that changes in oxygen may be signaled by changes in redox status.