1149 A Pilot Quality Improvement (QI) Study To Assess Whether Bilevel Positive Airway Pressure (bipap) Support In Acute Ischemic Stroke Patients With Sleep Disordered Breathing, Can Improve Neurological Recovery During Acute Stroke Care

Introduction

Obstructive sleep apnea (OSA) has been associated with adverse outcomes in patients with stroke. While data is limited, it suggests that treatment of OSA may improve neurological recovery. With this quality improvement (QI) project, we aim to develop an interprofessional-team workflow process for screening and correction of OSA in acute ischemic stroke, with the goal to improve outcomes of neurological recovery.

Methods

This is an ongoing study to screen all eligible patients admitted to JFK Medical Center stroke unit, with MRI-proven Supratentorial acute ischemic stroke. The patients are screened using an overnight Pulse Oximetry test. A 3% oxygen desaturation index (ODI) of ≥10/hr or 4% ODI of ≥ 5/hr is considered at high risk for OSA. Such Patients will receive nocturnal Auto-adjusting BIPAP therapy during their acute care stay, for up to 5 days, for at least 4 hours per night. Eligible Patients who refused BiPAP therapy or were non-compliant will be considered as a controls. Baseline NIH stroke scale (NIHSS), and bilateral MCA mean flow velocity (MFV) in the morning, by transcranial doppler (TCD) will be assessed at baseline for cases and controls, and after BiPAP therapy, for the case group. The two groups of patients will also be compared in terms of Modified Rankin Scale at time of discharge and at phone follow-up after 6 weeks.

Results

Between Oct 17th, 2019 to current, 15 patients were admitted to the stroke unit with MRI confirmed stroke. Ages ranged from 34 - 88 years (average age 66.5 years). 8 patients (60%) were female. Of those, 6 patients consented to being screened for OSA. Of these, 1 had 4%ODI >5/hr, and therefore received treatment with BIPAP. However, compliance was < 4 hrs on 2 consecutive nights.

Conclusion

This is ongoing QI project and results will be available after few more months of continued recruitment.

Support

Auto-adjusting BIPAP machines were provided by RESMED.

Substrate-Induced Facilitated Dissociation of the Competitive Inhibitor from the Active Site of O-Acetyl Serine Sulfhydrylase Reveals a Competitive-Allostery Mechanism

By classical competitive antagonism, a substrate and competitive inhibitor must bind mutually exclusively to the active site. The competitive inhibition of O-acetyl serine sulfhydrylase (OASS) by the C-terminus of serine acetyltransferase (SAT) presents a paradox, because the C-terminus of SAT binds to the active site of OASS with an affinity that is 4-6 log-fold (10⁴-10⁶) greater than that of the substrate. Therefore, we employed multiple approaches to understand how the substrate gains access to the OASS active site under physiological conditions. Single-molecule and ensemble approaches showed that the active site-bound high-affinity competitive inhibitor is actively dissociated by the substrate, which is not consistent with classical views of competitive antagonism. We employed fast-flow kinetic approaches to demonstrate that substrate-mediated dissociation of full length SAT-OASS (cysteine regulatory complex) follows a noncanonical "facilitated dissociation" mechanism. To understand the mechanism by which the substrate induces inhibitor dissociation, we resolved the crystal structures of enzyme·inhibitor·substrate ternary complexes. Crystal structures reveal a competitive allosteric binding mechanism in which the substrate intrudes into the inhibitor-bound active site and disengages the inhibitor before occupying the site vacated by the inhibitor. In summary, here we reveal a new type of competitive allosteric binding mechanism by which one of the competitive antagonists facilitates the dissociation of the other. Together, our results indicate that "competitive allostery" is the general feature of noncanonical "facilitated/accelerated dissociation" mechanisms. Further understanding of the mechanistic framework of "competitive allosteric" mechanism may allow us to design a new family of "competitive allosteric drugs/small molecules" that will have improved selectivity and specificity as compared to their competitive and allosteric counterparts.

Pharmacological Characterization of ZYAN1, a Novel Prolyl Hydroxylase Inhibitor for the Treatment of Anemia

Prolyl hydroxylase (PHD) inhibitors stabilize hypoxia inducible factor (HIF), and exert antianemic effect by potentiating erythropoietin (EPO) expression and down-regulation of hepcidin. ZYAN1 is a novel PHD inhibitor under clinical development for the treatment of anemia. The pharmacodynamic effects of acute and chronic dosing of ZYAN1 were assessed in normal and 5/6 nephrectomized Wistar rats. The effect of ZYAN1 was also investigated in cisplatin-induced anemia using C57 mice. Acute treatment with ZYAN1 increased circulating EPO levels (10.3 ± 3.7 and 40.0 ± 8.5 fold rise at 15 and 30 mg/kg, respectively), reticulocyte count (4.2 ± 0.5 and 6.0 ± 0.2 fold rise at 15 and 30 mg/kg, respectively) and stabilized HIF (28% increase at 45 mg/kg) in normal rats. Nephrectomized rats showed similar dose-related pharmacodynamic effects. In a 28-day study in nephrectomized rats, ZYAN1 administered every alternate day, caused increase in hemoglobin (1.9 ± 0.3 and 2.5 ± 0.4 g/dL) and RBC count (10.7 ± 4.0 and 14.0 ± 4.1%) at 15 and 30 mg/kg respectively. In cisplatin-treated mice also an increase in hemoglobin (3.4 ± 0.2 and 5.9 ± 0.2 g/dL) and RBC count (22.5 ± 2.2 and 37.3 ± 1.7%) at 15 and 30 mg/kg respectively was observed. ZYAN1's effects on hemoglobin and RBC count were distinct from darbepoietin. ZYAN1 demonstrated hematinic potential by combined effects on EPO release and efficient iron utilization. The efficacy of ZYAN1 in disease models of different etiologies suggests that it will be useful in treating wide spectrum of anemia patients.

Co-factor binding confers substrate specificity to xylose reductase from Debaryomyces hansenii

Binding of substrates into the active site, often through complementarity of shapes and charges, is central to the specificity of an enzyme. In many cases, substrate binding induces conformational changes in the active site, promoting specific interactions between them. In contrast, non-substrates either fail to bind or do not induce the requisite conformational changes upon binding and thus no catalysis occurs. In principle, both lock and key and induced-fit binding can provide specific interactions between the substrate and the enzyme. In this study, we present an interesting case where cofactor binding pre-tunes the active site geometry to recognize only the cognate substrates. We illustrate this principle by studying the substrate binding and kinetic properties of Xylose Reductase from Debaryomyces hansenii (DhXR), an AKR family enzyme which catalyzes the reduction of carbonyl substrates using NADPH as co-factor. DhXR reduces D-xylose with increased specificity and shows no activity towards "non-substrate" sugars like L-rhamnose. Interestingly, apo-DhXR binds to D-xylose and L-rhamnose with similar affinity (K(d)∼5.0-10.0 mM). Crystal structure of apo-DhXR-rhamnose complex shows that L-rhamnose is bound to the active site cavity. L-rhamnose does not bind to holo-DhXR complex and thus, it cannot competitively inhibit D-xylose binding and catalysis even at 4-5 fold molar excess. Comparison of K(d) values with K(m) values reveals that increased specificity for D-xylose is achieved at the cost of moderately reduced affinity. The present work reveals a latent regulatory role for cofactor binding which was previously unknown and suggests that cofactor induced conformational changes may increase the complimentarity between D-xylose and active site similar to specificity achieved through induced-fit mechanism.

Mass spectrometry assay for studying kinetic properties of dipeptidases: characterization of human and yeast dipeptidases

Chemical modifications of substrate peptides are often necessary to monitor the hydrolysis of small bioactive peptides. We developed an electrospray ionization mass spectrometry (ESI-MS) assay for studying substrate distributions in reaction mixtures and determined steady-state kinetic parameters, the Michaelis-Menten constant (K(m)), and catalytic turnover rate (V(max)/[E](t)) for three metallodipeptidases: two carnosinases (CN1 and CN2) from human and Dug1p from yeast. The turnover rate (V(max)/[E](t)) of CN1 and CN2 determined at pH 8.0 (112.3 and 19.5s(-1), respectively) suggested that CN1 is approximately 6-fold more efficient. The turnover rate of Dug1p for Cys-Gly dipeptide at pH 8.0 was found to be slightly lower (73.8s(-1)). In addition, we determined kinetic parameters of CN2 at pH 9.2 and found that the turnover rate was increased by 4-fold with no significant change in the K(m). Kinetic parameters obtained by the ESI-MS method are consistent with results of a reverse-phase high-performance liquid chromatography (RP-HPLC)-based assay. Furthermore, we used tandem MS (MS/MS) analyses to characterize carnosine and measured its levels in CHO cell lines in a time-dependent manner. The ESI-MS method developed here obviates the need for substrate modification and provides a less laborious, accurate, and rapid assay for studying kinetic properties of dipeptidases in vitro as well as in vivo.