Shift In P50 Research Articles

An increase in xylem embolism resistance of grapevine leaves during the growing season is coordinated with stomatal regulation, turgor loss point and intervessel pit membranes.

Although xylem embolism resistance is traditionally considered as static, we hypothesized that in grapevine (Vitis vinifera) leaf xylem becomes more embolism-resistant over the growing season. We evaluated xylem architecture, turgor loss point (ΨTLP ) and water potentials leading to 25% of maximal stomatal conductance (gs25 ) or 50% embolism in the leaf xylem (P50 ) in three irrigation treatments and at three time points during the growing season, while separating the effects of leaf age and time of season. Hydraulic traits acclimated over the growing season in a coordinated manner. Without irrigation, ΨTLP , gs25 , and P50 decreased between late May and late August by 0.95, 0.77 and 0.71MPa, respectively. A seasonal shift in P50 occurred even in mature leaves, while irrigation had only a mild effect (<0.2MPa) on P50 . Vessel size and pit membrane thickness were also seasonally dynamic, providing a plausible explanation for the shift in P50 . Our findings provide clear evidence that grapevines can modify their hydraulic traits along a growing season to allow lower xylem water potential, without compromising gas exchange, leaf turgor or xylem integrity. Seasonal changes should be considered when modeling ecosystem vulnerability to drought or comparing datasets acquired at different phenological stages.

Rejuvenation solution as an adjunct cold storage solution maintains physiological haemoglobin oxygen affinity during early-storage period of red blood cells.

Red blood cell (RBC) units accumulate morphologic and metabolic lesions during storage before transfusion. Pyruvate-inosine-phosphate-adenine (PIPA) solutions (Rejuvesol, Biomet, Warsaw, IN) can be incubated with RBC units to mitigate storage lesions. This study proposes a PIPA treatment process, termed cold 'rejuvenation', using Rejuvesol as an adjunct additive solution, to prevent biomechanical storage lesions while avoiding the 1h PIPA incubation required with standard PIPA treatment. We compared the efficacy of cold to standard 'rejuvenation' in improving metabolic lesions that occur during cold storage of RBCs, without altering function. Twelve leucoreduced, A-positive RBC units were obtained. Each unit was aliquoted into either control (standard storage), washed (W), standard rejuvenation (SR) or cold rejuvenation (CR) groups, the latter two requiring washing. A volume-adjusted dose of Rejuvesol was instilled into the CR group upon receipt (Day 3). After 15days of storage, p50, RBC deformability, in-bag haemolysis and mechanical fragility were analysed. 'Any treatment' is defined as W, SR and CR, with comparisons in reference to control. Higher p50s were seen in rejuvenated groups (>30mmHg vs. <19mmHg; P<0·0001). Any treatment significantly increased elongation index (P=0·034) but did not significantly increase in-bag haemolysis (P=0·062). Mechanical fragility was not significantly different between groups (P=0·055) at baseline, but the control (CTL) group was more fragile after 2h in a cardiac bypass simulation than any treatment (P<0·0001). This study demonstrates that rejuvenation (standard or cold) prevents the leftward p50 shift of storage lesions without detrimental effect on RBC deformity, in-bag haemolysis or mechanical fragility.

Human Neuroglobin Functions as a Redox-regulated Nitrite Reductase

Neuroglobin is a highly conserved hemoprotein of uncertain physiological function that evolved from a common ancestor to hemoglobin and myoglobin. It possesses a six-coordinate heme geometry with proximal and distal histidines directly bound to the heme iron, although coordination of the sixth ligand is reversible. We show that deoxygenated human neuroglobin reacts with nitrite to form nitric oxide (NO). This reaction is regulated by redox-sensitive surface thiols, cysteine 55 and 46, which regulate the fraction of the five-coordinated heme, nitrite binding, and NO formation. Replacement of the distal histidine by leucine or glutamine leads to a stable five-coordinated geometry; these neuroglobin mutants reduce nitrite to NO ∼2000 times faster than the wild type, whereas mutation of either Cys-55 or Cys-46 to alanine stabilizes the six-coordinate structure and slows the reaction. Using lentivirus expression systems, we show that the nitrite reductase activity of neuroglobin inhibits cellular respiration via NO binding to cytochrome c oxidase and confirm that the six-to-five-coordinate status of neuroglobin regulates intracellular hypoxic NO-signaling pathways. These studies suggest that neuroglobin may function as a physiological oxidative stress sensor and a post-translationally redox-regulated nitrite reductase that generates NO under six-to-five-coordinate heme pocket control. We hypothesize that the six-coordinate heme globin superfamily may subserve a function as primordial hypoxic and redox-regulated NO-signaling proteins.

Pharmacokinetics (PK) of RSR13 (efaproxiral) predict survival in patients with brain metastases randomized to receive whole brain radiation therapy (WBRT) with or without RSR13 (REACH RT-009)

1561 Background: 538 patients with brain metastases from selected solid tumors were randomized in a study of standard WBRT (30 Gy in 10 fractions) and supplemental oxygen with or without the radiation sensitizer RSR13 (efaproxiral) (Control n=267, RSR13 n=271). A non-significant improvement in MST was seen in favor of the RSR13 arm when results were analyzed by undajusted log-rank. The study showed a survival advantage for RSR13-treated patients versus controls after adjusting for imbalances in prognostic factors (Cox multiple regression) with the patients with breast cancer deriving the largest benefit from RSR13. Since a clear PK/Pharmacodynamic (PK = RSR13 concentration in RBCs and Pharmacodynamic = p50 shift) correlation had been established for RSR13 in previous studies, PK analyses were incorporated in the design of the present study. Methods: Blood samples were drawn for RSR13 PK analyses on Day 1 of RSR13 and at least once during the second week of RSR13 therapy. 188 patients had at least 2 PK determinations, 64 had 1 PK determination and 19 had no PK evaluation. Results: Higher PK were observed in patients with higher body weight and in women. Patients were assigned to 1 of 5 groups based on the number of WBRT fractions and the number of RSR13 doses received, as shown in the table below. Conclusions: These analyses reveal that patients with RSR13 concentrations in RBCs that reached optimal levels had a better outcome than those patients who did not. A clear correlation between PK, number of RSR13 doses, and MST was established. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Allos Therapeutics, Inc. Allos Therapeutics, Inc. Allos Therapeutics, Inc.

Pharmacokinetics (PK) of RSR13 (efaproxiral) predict survival in patients with brain metastases randomized to receive whole brain radiation therapy (WBRT) with or without RSR13 (REACH RT-009)

1561 Background: 538 patients with brain metastases from selected solid tumors were randomized in a study of standard WBRT (30 Gy in 10 fractions) and supplemental oxygen with or without the radiation sensitizer RSR13 (efaproxiral) (Control n=267, RSR13 n=271). A non-significant improvement in MST was seen in favor of the RSR13 arm when results were analyzed by undajusted log-rank. The study showed a survival advantage for RSR13-treated patients versus controls after adjusting for imbalances in prognostic factors (Cox multiple regression) with the patients with breast cancer deriving the largest benefit from RSR13. Since a clear PK/Pharmacodynamic (PK = RSR13 concentration in RBCs and Pharmacodynamic = p50 shift) correlation had been established for RSR13 in previous studies, PK analyses were incorporated in the design of the present study. Methods: Blood samples were drawn for RSR13 PK analyses on Day 1 of RSR13 and at least once during the second week of RSR13 therapy. 188 patients had at least 2 PK determinations, 64 had 1 PK determination and 19 had no PK evaluation. Results: Higher PK were observed in patients with higher body weight and in women. Patients were assigned to 1 of 5 groups based on the number of WBRT fractions and the number of RSR13 doses received, as shown in the table below. Conclusions: These analyses reveal that patients with RSR13 concentrations in RBCs that reached optimal levels had a better outcome than those patients who did not. A clear correlation between PK, number of RSR13 doses, and MST was established. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Allos Therapeutics, Inc. Allos Therapeutics, Inc. Allos Therapeutics, Inc.

The oxygen dissociation curve: quantifying the shift.

An oxyhaemoglobin dissociation curve (ODC) quantifies the most important function of red blood cells and that is the affinity for oxygen and its delivery to the tissues. Oxygen affinity for haemoglobin plays a critical role in the delivery of oxygen to the tissues and is changed by shifting to the left or right. A shift to the left implies an increased oxygen affinity and, hence, tighter binding due to the higher oxygen saturation in relation to the pO2. On the other hand, a shift to the right corresponds to a decreased oxygen affinity and easier release of oxygen to the tissues. It is well known that the ODC shifts in response to changes in pH, pCO2 and 2,3 diphosphoglycerate. However, how much the ODC shifts has never been quantified. Arterial and venous blood gases were taken during cardiopulmonary bypass and two indices were used to quantify the shift of the ODC; the p50 shift and the SO2 difference. Arterial blood shifted to the right by 4 +/- 0.1 mmHg at a pH of 7.24 and shifted to the left by -3.5 +/- 0.05 mmHg at a pH of 7.51. The change in arterial saturation was minimal, rising by 0.8% and dropping by -5% and did not correlate to p50 shifting and changes in pH, but demonstrated changes dependent on the concentration of dyshaemoglobins. The venous blood exhibited a greater range of p50 shifting at each pH value. At a pH of 7.24, the p50 shifted to the right by 4.8 +/- 2 mmHg and at a pH of 7.51 the p50 shifted to the left by -4 +/- 1.8 mmHg. Unlike the arterial blood, the change in saturation correlated well to p50 shifting. It is shown here for the first time how much the curve shifts with changes in pH and how this may be used to evaluate treatment strategies.

Allosteric Modification of Oxygen Delivery by Hemoglobin

Hemoglobin affinity for oxygen is altered by pH, temperature, and high altitude, making oxygen more readily available to the tissues. RSR13 (Allos Therapeutics, Denver, CO), an analog of the drugs clofibrate and bezofibrate, causes a dose-dependent, rightward shift of the oxygen dissociation curve in animals and humans. We tested the safety, pharmacodynamic, and pharmacokinetics of RSR13, an allosteric modifier of hemoglobin, in patients having general surgery in a prospective, randomized, double-blinded, placebo-controlled, dose-escalation clinical trial. After the induction of general anesthesia with endotracheal intubation, 26 patients who consented were randomly assigned to receive an infusion of RSR13 or placebo (2:1) in an ascending dose scheme. Doses studied were 10, 20, 30, 40, 50, 60, 75, and 100 mg/kg infused for 30–60 minutes. Samples were taken for determination of RSR13 concentration in plasma, red blood cells, and urine, as well as for determination of the p50 in blood by using three-point tonometry at frequent intervals after the infusion of the study drug. The RSR13 administration resulted in a dose-dependent rightward shift of the oxygen dissociation curve, with the target p50 shift of 10 mm Hg achieved at the 75- and 100-mg/kg doses. No differences were seen between RSR13 and placebo groups in laboratory or hemodynamic findings, with the exception of a transient, limited increase in serum creatinine in 3 patients who received RSR13. These increases peaked at 48 h (2.2, 3.5, and 4.5 mg/dL respectively), were not associated with oliguria, did not require treatment, and did not prolong hospitalization in any patient. The reasons for the unexplained increases in serum creatinine were not evident, but potentially included surgery itself (nephrectomy), patient condition, or the concomitant administration of renally cleared medications or drugs that affect renal blood flow.

Perioperative Myocardial Ischemia: Pathophysiology and Does it Really Matter

Perioperative Myocardial Ischemia: Pathophysiology and Does it Really Matter

Effect of nitric oxide and nitric oxide donors on red blood cell oxygen transport.

A mechanism has been proposed in which nitric oxide (NO) may bind to cysteine beta93 and be transported by haemoglobin from the lungs to the tissues and modify vascular tone. In addition, it has been reported that treatment of sickle cell anaemia blood with 80 p.p.m. NO gas in air shifts the oxygen affinity, as measured by P50 to the left. We exposed normal and sickle cell anaemia blood to 80 p.p.m. NO in air for 1 h in vitro and found no change in P50 of either normal or sickle cell blood. In addition, we exposed normal and sickle cell blood in buffer to aqueous NO (NO gas dissolved in buffer) at varying concentrations and found that the induced left shift in P50 correlates strongly and linearly with methaemoglobin formation. We also treated normal and sickle cell blood with other nitric oxide donors, such as sodium 2-(N, N-diethylamino)-diazenolate-2-oxide (DEANO), S-nitrosocysteine (CysNO) and sodium trioxodinitrate (OXINO, or Angeli's salt). In all cases, we found a dose-dependent increase in methaemoglobin that was strongly correlated with the dose-dependent P50 reduction. Our data do not support the report that low NO concentrations can selectively increase the oxygen affinity of sickle cell blood without affecting methaemoglobin levels significantly. NO, however, may have benefit in sickle cell disease by other mechanisms.

Effects of temporal variability on p50 and the gating ratio in schizophrenia: a frequency domain adaptive filter single-trial analysis.

Deficits in attention and cognition are common in schizophrenia. Using an auditory dual-click paradigm, a number of studies have found that, compared with normal controls, patients with schizophrenia show impaired inhibition, or gating, of repeated stimulation as measured by the average P50 evoked response to the second click. Since responses to many trials are collected to study the average response, fluctuations in the timing of the P50 response from trial to trial may influence the differences observed. We present a computerized, objective procedure that evaluates temporal variability in brain responses of patients with schizophrenia. Ten normal controls and 10 patients diagnosed with schizophrenia were studied using the dual-click procedure. For each single trial, the temporal shift in P50 that yielded the best alignment with the average P50 response was used to derive a measure of P50 temporal variability from trial to trial and to form P50 averages corrected for temporal variability. Patients with schizophrenia had significantly more temporal variability than normal controls. Correction for temporal variability in the P50 responses increased the size of P50 for both patients with schizophrenia and normal controls. Patients with schizophrenia had smaller P50 responses to the first click than controls and less inhibition to the second click before, but not after, correction for temporal variability. These findings suggest that temporal variability contributes significantly to the P50 response as measured using the gating procedure. The measure of temporal variability may provide a new index of inhibitory and attentional function in schizophrenia.

Analysis of P 50 and oxygen transport in patients after cardiac surgery

ObjectiveTo determine whether standard P50 after cardiac surgery decreases and whether decreased P50 is related to the transfusion of red blood cells (RBCs), acid-base changes, body temperature, oxygen parameters and/or duration of cardiopulmonary bypass (CPB).DesignPilot study in cardiac surgery patients.SettingUniversity hospital.Patients12 consecutive elective cardiac surgery patients.InterventionsBlood was taken before surgery, after CPB and in the intensive care unit until 18 h post-operatively. Cardiac output and oxygen consumption were measured. Buffy coat-poor RBCs were transfused, anticoagulated with citratephosphate-dextrose buffer and stored in saline-adenine-glucose-mannitol at 4°C, when haemoglobin was <5.6 mmol·l−1.Measurements and resultsStandard P50 was calculated from measured partial pressure of oxygen and of carbon dioxide, pH and oxygen saturation in mixed venous blood (SvO2) using the Severinghaus formula. Median length of RBC storage was 25 days. Standard P50 after surgery was significantly lower than baseline value (p=0.0001). The number of RBC units transfused and duration of CPB were conjointly associated with P50 (R 2=0.72). Patients who received more RBCs consumed more oxygen.ConclusionCardiac surgery patients receiving more RBC units have lower standard P50 and consume more oxygen. P50 decreased more when the CPB took longer. Because a decrease in P50 implies a low ratio of mixed venous oxygen tension (PvO2) to SvO2, a shift in P50 should be taken into account when using SvO2 as a measure of global oxygen availability. When a direct measurement of SvO2 is not available, PvO2 should be used instead of calculated SvO2.

Analysis of P50 and oxygen transport in patients after cardiac surgery.

To determine whether standard P50 after cardiac surgery decreases and whether decreased P50 is related to the transfusion of red blood cells (RBCs), acid-base changes, body temperature, oxygen parameters and/or duration of cardiopulmonary bypass (CPB). Pilot study in cardiac surgery patients. University hospital. 12 Consecutive elective cardiac surgery patients. Blood was taken before surgery, after CPB and in the intensive care unit until 18 h post-operatively. Cardiac output and oxygen consumption were measured. Buffy coat-poor RBCs were transfused, anticoagulated with citrate-phosphate-dextrose buffer and stored in saline-adenine-glucose-mannitol at 4 degrees C, when haemoglobin was < 5.6 mmol.l-1. Standard P50 was calculated from measured partial pressure of oxygen and of carbon dioxide, pH and oxygen saturation in mixed venous blood (SvO2) using the Severinghaus formula. Median length of RBC storage was 25 days. Standard P50 after surgery was significantly lower than baseline value (p = 0.0001). The number of RBC units transfused and duration of CPB were conjointly associated with P50 (R2 = 0.72). Patients who received more RBCs consumed more oxygen. Cardiac surgery patients receiving more RBC units have lower standard P50 and consume more oxygen. P50 decreased more when the CPB took longer. Because a decrease in P50 implies a low ratio of mixed venous oxygen tension (PvO2) to SvO2, a shift in P50 should be taken into account when using SvO2 as a measure of global oxygen availability. When a direct measurement of SvO2 is not available, PvO2 should be used instead of calculated SvO2.

HEMOGLOBIN OXYGEN AFFINITY IS INCREASED IN ERYTHROPOIETIC PROTOPORPHYRIA

Whole blood and hemolysates from seven normal and three erythropoietic protoporphyria patients were compared in terms of their hemoglobin function. The oxygen affinity (P50) of the erythropoietic protoporphyria hemolysates compared to normals (13.1 +/- 0.2 vs 17.5 +/- 0.3 mmHg; P < 0.001) and erythropoietic protoporphyria erythrocytes compared to normals (23.4 +/- 0.6 vs 27.1 +/- 0.5 mmHg; P < 0.001) were increased while oxygen-binding cooperativity (n-value of the Hill equation) were similar. We conclude that hemoglobin function in erythropoietic protoporphyria patients is altered, but without pathophysiologic consequences. Because hemoglobin in which protoporphyrin IX substitutes for heme has a low oxygen affinity, our findings of a higher than normal affinity in erythropoietic protoporphyria red cells and hemolysates may indirectly support the findings by others that protoporphyrin IX binds to hemoglobin at non-heme-binding sites. In addition, based on the effect of other abnormal hemoglobins, this shift in P50 will decrease any tendency for anemia in erythropoietic protoporphyria patients.

The effect of short-term oxygen supplementation on oxygen hemoglobin affinity in patients with chronic obstructive pulmonary disease.

In 12 hypoxemic patients with chronic obstructive pulmonary disease, the partial pressure of oxygen at which hemoglobin is 50% saturated (P50) and levels of 2,3-diphosphoglycerate (2,3-DPG) were determined under 3 study conditions: (1) while breathing room air, (2) during oxygen supplementation for 72 h sufficient to increase PaO2 above 70 mmHg, and (3) at 72 h after the period of oxygen supplementation. The data showed that in the control period in hypoxemic (PaO2, 52 +/- 6 mmHg), mildly hypercapnic (PaCO2, 47 +/- 6 mmHg) patients with a borderline elevation of pH (7.42 +/- 0.03), there was an increase in P50 (28.6 +/- 1.6 versus a normal value of 26.5 +/- 1; p less than 0.005), and a concomitant increase in 2,3-DPG (19.02 +/- 1.77 mg/g Hb versus a normal value of 13.52 +/- 1.27; p less than 0.005). Nine patients received oxygen for 24 h, and 5 received oxygen for 72 h. In these 5 patients, oxygen supplementation resulted in a shift in P50 to a normal value of 26.7 +/- 1.8 (this value was different from the patients' level while breathing room air and not different from that of the normoxemic control subjects) and a decrease in 2,3-DPG toward but not to a normal value (16.34 +/- 1.92; p less than 0.01). This shift in P50 to the left could be related to the decrease in 2,3-DPG. Accordingly, in patients with COPD who are treated with supplemental oxygen, the net effect on oxygen transport would be a function of the changes produced in PaO2 versus those in hemoglobin-oxygen affinity.(ABSTRACT TRUNCATED AT 250 WORDS)

PHOTOSENSITIZED SHIFT IN THE O2 DISSOCIATION CURVE OF FETAL BLOOD

Abstract. Ostrea, E. Jr., and Odell, G. (Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA). Photosensitized shift in the O2 dissociation curve of fetal blood. Acta Paediatr Scand, 63: 341, 1974.–The exposure of fetal erythrocytes to blue light in the presence of bilirubin was associated with a significant decrease in the affinity of fetal cells for O2, (δP50) at pH 7.4=+3.17± 0.68 mmHg. This change was not observed with either adult erythrocytes or hemolysates of fetal and adult red cells. Associated with the shift in P50, there was a decrease in the Na+, K+ ‐ATP'ase of the irradiated erythrocytes and no electrophoretic evidence of alteration in the fetal hemoglobin. The results suggest that the shift in the O2 dissociation curve represents an additional manifestation of photodynamic membrane injury and the stroma of fetal erythrocytes influence their oxygen affinity.