Zona pellucida removal by acid Tyrode's solution affects pre- and post-implantation development and gene expression in mouse embryos†.

The zona pellucida plays a crucial role in the process of fertilization to early embryonic development, including cellular arrangement and communication between blastomeres. However, little is known regarding the role of the zona pellucida in pre- and post-implantation embryonic development associated with gene expression. We investigated the effect of zona pellucida removal on pre- and post-implantation development of mouse embryos. After zona pellucida removal of two-cell stage embryos was performed by acid Tyrode's solution, which is commonly used for zona pellucida treatment, compaction occurred earlier in zona pellucida-free than zona pellucida-intact embryos. In addition, the expression of differentiation-related genes in the inner cell mass and trophectoderm was significantly altered in zona pellucida-free blastocyst compared with zona pellucida-intact embryos. After embryo transfer, the rate of implantation and live fetuses was lower in zona pellucida-free embryos than in control embryos, whereas the fetal weight at E17.5 was not different. However, placental weight significantly increased in zona pellucida-free embryos. RNA-sequencing analysis of the placenta showed that a total of 473 differentially expressed genes significantly influenced the biological process. The present study suggests that zona pellucida removal by acid Tyrode's solution at the two-cell stage not only disturbs the expression pattern of inner cell mass-/trophectoderm-related genes but affects the post-implantation development of mouse embryos. Overall, this study provides deeper insight into the role of the zona pellucida during early embryonic development and the viability of post-implantation development.

Pharmacokinetic and pharmacodynamic profiles of a novel phospholipid-aspirin complex liquid formulation and low dose enteric-coated aspirin: results from a prospective, randomized, crossover study.

Low dose enteric-coated aspirin (EC-ASA) is routinely used for secondary cardiovascular event prevention. However, absorption of EC tablets is poor, which can result in subtherapeutic antiplatelet effects. Phospholipid-aspirin liquid filled capsules (PL-ASA) are a novel FDA-approved immediate-release formulation designed to reduce gastrointestinal (GI) injury by limiting direct contact with the stomach lining. We compared the pharmacokinetic (PK) and pharmacodynamic (PD) profiles of PL-ASA versus EC-ASA at a low dose. This randomized, open-label, crossover study assessed PK and PD following a single 81-mg dose of PL-ASA versus EC-ASA under fasting conditions in 36 volunteers without cardiovascular disease between 18 and 75 years of age. Volunteers were randomly assigned 1:1 to either PL-ASA then EC-ASA or vice versa with a minimum 14-day washout. Assessments included PK parameters for acetylsalicylic acid and salicylic acid, platelet aggregation in response to arachidonic acid (AA), and serum thromboxane B2 (TxB2) assessments over 24 h. PL-ASA was rapidly absorbed. PL-ASA reached Tmax 3 h earlier (1.01 vs. 4.00 h, p < 0.0001), with almost double the Cmax (720 vs. 368 ng/mL, p < 0.0001) and overall 44% higher exposure of acetylsalicylic acid (AUC0-t: 601 vs. 416 h*ng/mL, p = 0.0013) compared with EC-ASA. Within 1 h of dosing, PL-ASA achieved significantly lower residual platelet aggregation, which persisted for the full 24 h (median AA-LTA was 47% with PL-ASA vs. 80.5% with EC-ASA; p = 0.0022 at hour-24). Treatment with PL-ASA also resulted in significantly lower serum TxB2 concentrations at each time point compared with EC-ASA (all p-values < 0.05). PL-ASA resulted in faster and more complete aspirin absorption paralleled by more prompt and potent platelet inhibition compared with EC-ASA after a single 81 mg dose. PL-ASA represents an attractive novel aspirin formulation for the secondary prevention of cardiovascular events.Clinical Trial Registration ClinicalTrials.gov identifier: NCT04811625.

The use of a two-step removal protocol and optimized culture conditions improve development and quality of zona free mouse embryos.

The zona pellucida (ZP) plays an important role in both the fertilization and embryonic development. For the successful handling of early stage blastomeres for differentiation analysis, the production of identical twins or quadruplets, nuclear transfer or gene introduction requires the removal of the ZP (ZPR). Although single use of either acidic Tyrode's solution or pronase are commonly used for ZPR, long-term exposure to these agents can result in the inhibition of development with the collapse of the three-dimensional blastomere structure. Here, we demonstrate the benefits of using a two-step combined ZPR method, which relies upon a customized well-of-well (cWOW) system with smaller well size, on developmental competence and the quality of the zona free (ZF) mouse embryos. We first isolated 2-cell embryos using acid Tyrode's solution and then cultured these embryos using either commercially available or cWOW, which had a smaller microwell size. The rate of blastocyst was significantly increased by use of cWOW when compared to other culture systems. Then we evaluated the use of a two-step ZPR protocol, relying on acid Tyrode's solution and proteinase K, and subsequent culture in the cWOW system. Although acid Tyrode's solution treatment alone reduced ZPR time, blastomere morphology became wrinkled, significant decrease in blastocyst rate associated with increased number of apoptotic cells and increased expression of apoptosis-related genes were observed. Using proteinase K alone increased ZPR time and significantly decreased the blastocyst rate, but did not induce an increase in apoptotic cell number or apoptosis-related gene expression. In contrast, two-step method significantly reduced ZPR time and improved blastocyst rate by increasing the total number of cells in these wells an reducing the number of apoptotic cells in these experiments. These results suggest that the two-step ZPR protocol is beneficial for reducing the toxic effects of zona removal on ZF embryo development and quality when combined with a suitable culture system.

Bioavailability of aspirin in fasted and fed states of a novel pharmaceutical lipid aspirin complex formulation.

Dyspeptic symptoms are common with aspirin and clinicians frequently recommend that it be taken with food to reduce these side effects. However, food can interfere with absorption, especially with enteric-coated aspirin formulations. We evaluated whether food interferes with the bioavailability of a new, pharmaceutical lipid-aspirin complex (PL-ASA) liquid-filled capsule formulation. In this randomized, open label, crossover study, 20 healthy volunteers fasted for ≥ 10 h and then randomized as either "fasted", receiving 650 mg of PL-ASA, or as "fed", with a standard high-fat meal and 650 mg of PL-ASA 30 min later. After a washout of 7 days, participants crossed over to the other arm. The primary outcome was comparison of PK parameters of the stable aspirin metabolite salicylic acid (SA) between fasted and fed states. Mean age of participants was 36.8 years and 55% were male. The ratios for the fed to fasted states of the primary SA PK parameters of AUC0-t and AUC0-∞ were 88.7% and 88.8% respectively, with 90% confidence intervals between 80 and 125%, which is consistent with FDA bioequivalence guidance. Mean peak SA concentration was about 22% lower and occurred about 1.5 h later in the fed state. Food had a modest effect on peak SA levels and the time required to reach them after PL-ASA administration, but did not impact the extent of exposure (AUC) compared with intake in a fasted state. These data demonstrate that PL-ASA may be co-administered with food without significant impact on aspirin bioavailability.Clinical Trial Registration:http://www.clinicaltrials.gov Unique Identifier: NCT01244100.

RGB-D SLAM Using Point-Plane Constraints for Indoor Environments.

Pose estimation and map reconstruction are basic requirements for robotic autonomous behavior. In this paper, we propose a point-plane-based method to simultaneously estimate the robot's poses and reconstruct the current environment's map using RGB-D cameras. First, we detect and track the point and plane features from color and depth images, and reliable constraints are obtained, even for low-texture scenes. Then, we construct cost functions from these features, and we utilize the plane's minimal representation to minimize these functions for pose estimation and local map optimization. Furthermore, we extract the Manhattan World (MW) axes on the basis of the plane normals and vanishing directions of parallel lines for the MW scenes, and we add the MW constraint to the point-plane-based cost functions for more accurate pose estimation. The results of experiments on public RGB-D datasets demonstrate the robustness and accuracy of the proposed algorithm for pose estimation and map reconstruction, and we show its advantages compared with alternative methods.

A Retrospective Cohort Analysis Shows that Coadministration of Minocycline with Colistin in Critically Ill Patients Is Associated with Reduced Frequency of Acute Renal Failure.

Nonclinical studies have suggested that oxidative damage, caspase-mediated apoptosis, and inducible nitric oxide synthase levels may be involved in the pathogenesis of colistin (CST)-associated acute renal failure. MIN inhibits caspase 1, caspase 3, and inducible nitric oxide synthase, leading to the hypothesis that coadministration of CST with MIN (CST-MIN) may reduce the incidence of acute renal failure as well as produce additive or synergistic antimicrobial effects. A multicenter retrospective cohort study was conducted using the Premier Research database to examine the impact of CST-MIN on acute renal failure. Inclusion criteria were as follows: age of ≥18 years, intensive care unit admission at CST initiation, primary International Classification of Diseases 9 (ICD-9) diagnosis of pneumonia or sepsis, nondialysis at hospital admission, and discharge between January 2010 and December 2015. ICD-9 code 584.XX or ICD-10 code N17 was used to define acute renal failure. Baseline comparisons, 1:8 propensity score matching, and confirmatory logistic regression analyses were conducted. In total, 4,817 patients received CST and met inclusion criteria; 93 received CST-MIN. Unadjusted frequency of acute renal failure was significantly lower in patients receiving CST-MIN than CST (11.8% versus 23.7%, P = 0.007). Similar results were seen in propensity score matching (12.0% versus 22.3%, P = 0.031) and logistic regression analyses (odds ratio of 0.403, P = 0.006). Mortalities and 30-day readmission rates were similar between groups. The acute renal failure rate was not impacted by prevalence of baseline renal disease. CST-MIN in critically ill patients may reduce CST-associated acute renal failure. Further evaluation of this combination in prospective clinical studies is warranted.

Cost implications of intraprocedural thrombotic events and bleeding in percutaneous coronary intervention: Results from the CHAMPION PHOENIX ECONOMICS Study.

BACKGROUND: Despite improvements in percutaneous coronary intervention (PCI), intraprocedural thrombotic events (IPTE) and bleeding complications occur and are prognostically important. These have not been included in prior economic studies. METHODS: PHOENIX ECONOMICS was a substudy of the CHAMPION PHOENIX trial, evaluating cangrelor during PCI. Hospital bills were reviewed from 1,171 patients enrolled at 22 of 63 US sites. Costs were estimated using standard methods including resource-based accounting, hospital billing data, and the Medicare fee schedule. Bleeding and IPTE, defined as abrupt vessel closure (transient or sustained), new/suspected thrombus, new clot on wire/catheter, no reflow, side-branch occlusion, procedural stent thrombosis or urgent need for CABG were identified. Costs were calculated according to whether a complication occurred and type of event. Multivariate analyses were used to estimate the incremental costs of IPTE and postprocedural events. RESULTS: IPTE occurred in 4.3% and were associated with higher catheterization laboratory and overall index hospitalization costs by $2,734 (95%CI $1,117, $4,351; P = 0.001) and $6,354 (95% CI $4,122, $8,586; P < 0.001), respectively. IPTE were associated with MI (35.4% vs. 3.6%; P < 0.001), out-of-laboratory stent thrombosis (4.2% vs. 0.1%; 0 = 0.005), ischemia driven revascularization (12.5% vs. 0.3%; P < 0.001), but not mortality (2.1% vs. 0.2%; P = 0.12) vs. no procedural thrombotic complication. By comparison, ACUITY minor bleeding increased hospitalization cost by $1,416 (95%CI = 312, $2,519; P = 0.012). ACUITY major bleeding increased cost of hospitalization by $7,894 (95%CI $4,154, $11,635; P < 0.001). CONCLUSIONS: IPTE and bleeding complications, though infrequent, are associated with substantial increased cost. These complications should be collected in economic assessments of PCI.

Carbapenem resistance, inappropriate empiric treatment and outcomes among patients hospitalized with Enterobacteriaceae urinary tract infection, pneumonia and sepsis.

BACKGROUND: Drug resistance among gram-negative pathogens is a risk factor for inappropriate empiric treatment (IET), which in turn increases the risk for mortality. We explored the impact of carbapenem-resistant Enterobacteriaceae (CRE) on the risk of IET and of IET on outcomes in patients with Enterobacteriaceae infections. METHODS: We conducted a retrospective cohort study in Premier Perspective database (2009-2013) of 175 US hospitals. We included all adult patients with community-onset culture-positive urinary tract infection (UTI), pneumonia, or sepsis as a principal diagnosis, or as a secondary diagnosis in the setting of respiratory failure, treated with antibiotics within 2 days of admission. We employed regression modeling to compute adjusted association of presence of CRE with risk of receiving IET, and of IET on hospital mortality, length of stay (LOS) and costs. RESULTS: Among 40,137 patients presenting to the hospital with an Enterobacteriaceae UTI, pneumonia or sepsis, 1227 (3.1%) were CRE. In both groups, the majority of the cases were UTI (51.4% CRE and 54.3% non-CRE). Those with CRE were younger (66.6+/-15.3 vs. 69.1+/-15.9 years, p < 0.001), and more likely to be African-American (19.7% vs. 14.0%, p < 0.001) than those with non-CRE. Both chronic (Charlson score 2.0+/-2.0 vs. 1.9+/-2.1, p = 0.009) and acute (by day 2: ICU 56.3% vs. 30.4%, p < 0.001, and mechanical ventilation 35.8% vs. 11.7%, p < 0.001) illness burdens were higher among CRE than non-CRE subjects, respectively. CRE patients were 3× more likely to receive IET than non-CRE (46.5% vs. 11.8%, p < 0.001). In a regression model CRE was a strong predictor of receiving IET (adjusted relative risk ratio 3.95, 95% confidence interval 3.5 to 4.5, p < 0.001). In turn, IET was associated with an adjusted rise in mortality of 12% (95% confidence interval 3% to 23%), and an excess of 5.2 days (95% confidence interval 4.8, 5.6, p < 0.001) LOS and $10,312 (95% confidence interval $9497, $11,126, p < 0.001) in costs. CONCLUSIONS: In this large US database, the prevalence of CRE among patients with Enterobacteriaceae UTI, pneumonia or sepsis was comparable to other national estimates. Infection with CRE was associated with a four-fold increased risk of receiving IET, which in turn increased mortality, LOS and costs.

Exploring second coordination sphere effects in nitric oxide synthase.

Second coordination sphere (SCS) effects in proteins are modulated by active site residues and include hydrogen bonding, electrostatic/dipole interactions, steric interactions, and π-stacking of aromatic residues. In Cyt P450s, extended H-bonding networks are located around the proximal cysteinate ligand of the heme, referred to as the 'Cys pocket'. These hydrogen bonding networks are generally believed to regulate the Fe-S interaction. Previous work identified the S(Cys) → Fe σ CT transition in the high-spin (hs) ferric form of Cyt P450cam and corresponding Cys pocket mutants by low-temperature (LT) MCD spectroscopy [Biochemistry 50:1053, 2011]. In this work, we have investigated the effect of the hydrogen bond from W409 to the axial Cys ligand of the heme in the hs ferric state (with H4B and L-Arg bound) of rat neuronal nitric oxide synthase oxygenase construct (nNOSoxy) using MCD spectroscopy. For this purpose, wt enzyme and W409 mutants were investigated where the H-bonding network with the axial Cys ligand is perturbed. Overall, the results are similar to Cyt P450cam and show the intense S(Cys) → Fe σ CT band in the LT MCD spectrum at about 27,800 cm-1, indicating that this feature is a hallmark of {heme-thiolate} active sites. The discovery of this MCD feature could constitute a new approach to classify {heme-thiolate} sites in hs ferric proteins. Finally, the W409 mutants show that the hydrogen bond from this group only has a small effect on the Fe-S(Cys) bond strength, at least in the hs ferric form of the protein studied here. Low-temperature MCD spectroscopy is used to investigate the effect of the hydrogen bond from W409 to the axial Cys ligand of the heme in neuronal nitric oxide synthase. The intense S(Cys) → Fe σ-CT band is monitored to identify changes in the Fe-S(Cys) bond in wild-type protein and W409 mutants.

Bivalirudin is associated with improved clinical and economic outcomes in heart failure patients undergoing percutaneous coronary intervention: Results from an observational database.

BACKGROUND: Outcomes with bivalirudin compare favorably with heparin ± GPIIb/IIIa receptor inhibition (heparin ± GPI) during percutaneous coronary intervention (PCI). Patients with congestive heart failure (CHF) have increased risk for complications. The objective was to investigate clinical and economic outcomes for bivalirudin ± GPI vs. heparin ± GPI among PCI patients with CHF. METHODS: Using the Premier Hospital Database, PCI patients with CHF were stratified by anticoagulant: bivalirudin, bivalirudin ± GPI, heparin and heparin ± GPI. The probability of receiving bivalirudin ± GPI was estimated using individual and hospital variables. Using propensity scores, each bivalirudin ± GPI patient was matched to a heparin ± GPI patient. The primary outcome was in-hospital death. Bleeding rates, transfusion, length of stay and in-hospital cost were ascertained. RESULTS: Overall, 116,313 patients at 315 hospitals received bivalirudin (n = 45,559) bivalirudin + GPI (n = 8,115), heparin (n = 27,972) or heparin + GPI (n = 34,667). Patients had STEMI (21.2%), NSTEMI (29.1%), unstable angina (16.6%), stable angina (5.7%) or other ischemic heart disease (24.2%). Of these, 79.1% of bivalirudin patients matched, resulting in 84,948 analyzed patients. Compared with heparin ± GPI patients, bivalirudin ± GPI patients had fewer deaths (3.3% vs. 3.9%; p < 0.0001), less clinically apparent bleeding (10.2% vs. 11.4%; p < 0.0001), clinically apparent bleeding with transfusion (2.7% vs. 3.2%, p <0.0001), and transfusion (8.5% vs. 9.8%, p < 0.0001). Patients receiving bivalirudin had shorter length of stay (6.3 vs. 6.8 days; p < 0.0001) and lower in-hospital cost (mean $26,706 vs. $27,166 [median $19,414 vs. $19,798]; p < 0.0001). In conclusion, this is the largest retrospective analysis of PCI patients with CHF and demonstrates bivalirudin ± GPI compared with heparin ± GPI is associated with lower inpatient rates of death, bleeding, and cost.

Multidrug resistance, inappropriate empiric therapy, and hospital mortality in Acinetobacter baumannii pneumonia and sepsis.

BACKGROUND: The relationship between multidrug resistance (MDR), inappropriate empiric therapy (IET), and mortality among patients with Acinetobacter baumannii (AB) remains unclear. We examined it using a large U.S. METHODS: We conducted a retrospective cohort study using the Premier Research database (2009-2013) of 175 U.S. hospitals. We included all adult patients admitted with pneumonia or sepsis as their principal diagnosis, or as a secondary diagnosis in the setting of respiratory failure, along with antibiotic administration within 2 days of admission. Only culture-confirmed infections were included. Resistance to at least three classes of antibiotics defined multidrug-resistant AB (MDR-AB). We used logistic regression to compute the adjusted relative risk ratio (RRR) of patients with MDR-AB receiving IET and IET's impact on mortality. RESULTS: Among 1423 patients with AB infection, 1171 (82.3 %) had MDR-AB. Those with MDR-AB were older (63.7 ± 15.4 vs. 61.0 ± 16.9 years, p = 0.014). Although chronic disease burden did not differ between groups, the MDR-AB group had higher illness severity than those in the non-MDR-AB group (intensive care unit 68.0 % vs. 59.5 %, p < 0.001; mechanical ventilation 56.2 % vs. 42.1 %, p < 0.001). Patients with MDR-AB were more likely to receive IET than those in the non-MDR-AB group (76.2 % MDR-AB vs. 13.8 % non-MDR-AB, p < 0.001). In a regression model, MDR-AB strongly predicted receipt of IET (adjusted RRR 5.5, 95 % CI 4.0-7.7, p < 0.001). IET exposure was associated with higher hospital mortality (adjusted RRR 1.8, 95 % CI 1.4-2.3, p < 0.001). CONCLUSIONS: In this large U.S. database, the prevalence of MDR-AB among patients with AB infection was > 80 %. Harboring MDR-AB increased the risk of receiving IET more than fivefold, and IET nearly doubled hospital mortality.

Cost implications of intraprocedural thrombotic events during PCI.

OBJECTIVES: We sought to estimate the direct costs (in-hospital and 30-day) associated with an intraprocedural thrombotic event (IPTE) among patients with non-ST-segment elevation acute coronary syndromes (NSTEACS) undergoing percutaneous coronary intervention (PCI). BACKGROUND: Patients with IPTE have higher rates of in-hospital and 30-day major adverse cardiac events than patients without IPTE. The extent to which IPTE also add to medical costs is unknown. METHODS: Hospital costs for patients in the ACUITY Trial were compared between patients with and without IPTE. Adjusted comparisons were performed using generalized linear models (GLMs). All costs are reported in 2012 US dollars. RESULTS: A total of 1,307 patients with both core laboratory-based angiographic assessment and detailed economic data were included in the final study population. IPTE occurred in 52 patients (4.0%). Median in-hospital costs were higher in patients with IPTE than in those without IPTE ($23,719 vs. $18,419, P = 0.01). Thirty-day median costs were also higher for IPTE patients ($23,719 vs. $19,556, P = 0.05). After adjusting for baseline differences, IPTE was associated with 19.5% (95% CI: [2.8-38.8%], P = 0.02) and 18.9% (95% CI: [1.2-39.7%], P = 0.04) increases in in-hospital and 30-day costs, respectively. These relative differences represent median increases of $3,592 in initial hospital costs and $3,696 in 30-day costs. CONCLUSIONS: The occurrence of IPTE during the index PCI in patients with NSTEACS is associated with substantial increases in-hospital and 30-day costs. These findings suggest that strategies to prevent IPTE may be associated with important cost offsets as well as improved clinical outcomes.

The effects of operating parameters on spiramycin removal by nanofiltration membrane.

Spiramycin removal from wastewater using four nanofiltration (NF) membranes (NF270, NF90, ESNA1-K1 and ESNA1-LF2-LD) was studied. The effects of operating pressure, feed temperature, feed concentration, cation and anion ions on the permeate flux rate and spiramycin rejection were investigated. The results show that increasing operating pressure resulted in the increase of both permeate flux and spiramycin rejection. The flux rate increased almost linearly with temperature, while the spiramycin rejection decreased. The permeate flux rate declined relatively with increasing feed concentration of spiramycin for NF270 and ESNA1-LF2-LD membranes compared with NF90 and ESNA1-K membranes. The presence of cations reduced spiramycin rejection, with the strength of influence for the NF270 NF membrane following the order Mg(2+)>Ca(2+)>K(+). The presence of anions also resulted in decreased spiramycin rejection, the strength of the effect following the order NO(3)(-)>Cl(-)>SO(4)(2-) for the NF270 membrane.

Effects of ion concentration and natural organic matter on arsenic(V) removal by nanofiltration under different transmembrane pressures.

The removal of As(V) from synthetic water was studied using four different nanofiltration (NF) membranes (ESNA-1-K1, NF270, ESNA-1-LF, and HODRA-CORE). The influences of ion concentration, transmembrane pressure (TMP), and the presence of natural organic matter (humic acid, HA) on the arsenic removal efficiency and permeate flux were investigated. The arsenic rejection of ESNA-1-LF was higher than those of the other membranes in all experiments (> 94%), and the HODRA-CORE membrane gave the lowest removal of arsenic (< 47%). An increase in the ion concentration in the feed solution and addition of HA decreased the arsenic rejection of the HODRA-CORE membrane. However, both increasing of the ion concentration and addition of HA made the rejection increased for the other membranes (ESNA-1-K1, NF270, and ESNA-1-LF). With increasing TMP, for all four NF membranes, increases in both arsenic rejection and permeate flux were observed. The permeate fluxes of the four NF membranes decreased to some extent after addition of HA to the solutions for operating time of 6 hr.

Persistent Nocardia beijingensis infection in a patient with postoperative abscess and misuse of antibiotics in China.

Here we describe the first case of abscess infection caused by Nocardia beijingensis in China. The patient was immunocompetent but suffered from postoperative abscess for 6 years. This study highlights the necessity of long-term infected foci to be thoroughly examined to identify the pathogen, as well as the importance of accurate Nocardia identification and antimicrobial susceptibility tests for understanding the pathogen's epidemiology, clinical significance, and treatment strategy.

Role of an isoform-specific substrate access channel residue in CO ligand accessibilities of neuronal and inducible nitric oxide synthase isoforms.

The rates of the bimolecular CO rebinding to the oxygenase domains of inducible and neuronal NOS proteins (iNOSoxy and nNOSoxy, respectively) after photolytic dissociation have been determined by laser flash photolysis. The following mutants at the isoform-specific sites (murine iNOSoxy N115L and rat nNOSoxy L337N, L337F) have been constructed to investigate role of the residues in the CO ligand accessibilities of the NOS isoforms. These residues are in the NOS distal substrate access channel. The effect of the (6R)-5,6,7,8-tetrahydrobiopterin (H(4)B) cofactor and l-arginine (Arg) substrate on the rates of CO rebinding have also been assessed. Addition of l-Arg to the iNOSoxy N115L mutant results in much faster CO rebinding rates, compared to the wild type. The results indicate that modifications to the iNOS channel in which the hydrophilic residue N115 is replaced by leucine (to resemble its nNOS cognate) open the channel somewhat, thereby improving access to the axial heme ligand binding position. On the other hand, introduction of a hydrophilic residue (L337N) or a bulky rigid aromatic residue (L337F) in the nNOS isoform does not significantly affect the kinetics profile, suggesting that the geometry of the substrate access pocket is not greatly altered. The bimolecular CO rebinding rate data indicate that the opening of the substrate access channel in the iNOS N115L mutant may be due to more widespread structural alterations induced by the mutation.

Role of an isoform-specific serine residue in FMN-heme electron transfer in inducible nitric oxide synthase.

In the crystal structure of a calmodulin (CaM)-bound FMN domain of human inducible nitric oxide synthase (NOS), the CaM-binding region together with CaM forms a hinge, and pivots on an R536(NOS)/E47(CaM) pair (Xia et al. J Biol Chem 284:30708-30717, 2009). Notably, isoform-specific human inducible NOS S562 and C563 residues form hydrogen bonds with the R536 residue through their backbone oxygens. In this study, we investigated the roles of the S562 and C563 residues in the NOS FMN-heme interdomain electron transfer (IET), the rates of which can be used to probe the interdomain FMN/heme alignment. Human inducible NOS S562K and C563R mutants of an oxygenase/FMN (oxyFMN) construct were made by introducing charged residues at these sites as found in human neuronal NOS and endothelial NOS isoforms, respectively. The IET rate constant of the S562K mutant is notably decreased by one third, and its flavin fluorescence intensity per micromole per liter is diminished by approximately 24 %. These results suggest that a positive charge at position 562 destabilizes the hydrogen-bond-mediated NOS/CaM alignment, resulting in slower FMN-heme IET in the mutant. On the other hand, the IET rate constant of the C563R mutant is similar to that of the wild-type, indicating that the mutational effect is site-specific. Moreover, the human inducible NOS oxyFMN R536E mutant was constructed to disrupt the bridging CaM/NOS interaction, and its FMN-heme IET rate was decreased by 96 %. These results demonstrated a new role of the isoform-specific serine residue of the key CaM/FMN(NOS) bridging site in regulating the FMN-heme IET (possibly by tuning the alignment of the FMN and heme domains).

Pulsed ENDOR determination of the arginine location in the ferrous-NO form of neuronal NOS.

Mammalian nitric oxide synthases (NOSs) are enzymes responsible for oxidation of L-arginine (L-Arg) to nitric oxide (NO). Mechanisms of reactions at the catalytic heme site are not well understood, and it is of current interest to study structures of the heme species that activates O(2) and transforms the substrate. The NOS ferrous-NO complex is a close mimic of the obligatory ferric (hydro)peroxo intermediate in NOS catalysis. In this work, pulsed electron-nuclear double resonance (ENDOR) was used to probe the position of the l-Arg substrate at the NO(•)-coordinated ferrous heme center(s) in the oxygenase domain of rat neuronal NOS (nNOS). The analysis of (2)H and (15)N ENDOR spectra of samples containing d(7)- or guanidino-(15)N(2) labeled L-Arg has resulted in distance estimates for the nearby guanidino nitrogen and the nearby proton (deuteron) at C(δ). The L-Arg position was found to be noticeably different from that in the X-ray crystal structure of nNOS ferrous-NO complex [Li et al. J. Biol. Inorg. Chem.2006, 11, 753-768], with the nearby guanidino nitrogen being ~0.5 Šcloser to, and the nearby H(δ) about 1 Šfurther from, the NO ligand than in the X-ray structure. The difference might be related to the structural constraints imposed on the protein by the crystal. Importantly, in spite of its closer position, the guanidino nitrogen does not form a hydrogen bond with the NO ligand, as evidenced by the absence of significant isotropic hfi constant for N(g1). This is consistent with the previous reports that it is not the L-Arg substrate itself that would most likely serve as a direct proton donor to the diatomic ligands (NO and O(2)) bound to the heme.

Mutation in the flavin mononucleotide domain modulates magnetic circular dichroism spectra of the iNOS ferric cyano complex in a substrate-specific manner.

We have obtained low-temperature magnetic circular dichroism (MCD) spectra for ferric cyano complexes of the wild type and E546N mutant of a human inducible nitric oxide synthase (iNOS) oxygenase/flavin mononucleotide (oxyFMN) construct. The mutation at the FMN domain has previously been shown to modulate the MCD spectra of the l-arginine-bound ferric iNOS heme (Sempombe, J.; et al. J. Am. Chem. Soc. 2009, 131, 6940-6941). The addition of l-arginine to the wild-type protein causes notable changes in the CN(-)-adduct MCD spectrum, while the E546N mutant spectrum is not perturbed. Moreover, the MCD spectral perturbation observed with l-arginine is absent in the CN(-) complexes incubated with N-hydroxy-L-arginine, which is the substrate for the second step of NOS catalysis. These results indicate that interdomain FMN-heme interactions exert a long-range effect on key heme axial ligand-substrate interactions that determine substrate oxidation pathways of NOS.