Improving production of Streptomyces griseus trypsin for enzymatic processing of insulin precursor.

BACKGROUND: Trypsin has many applications in food and pharmaceutical manufacturing. Although commercial trypsin is usually extracted from porcine pancreas, this source carries the risks of infectivity and immunogenicity. Microbial Streptomyces griseus trypsin (SGT) is a prime alternative because it possesses efficient hydrolysis activity without such risks. However, the remarkable hydrolysis efficiency of SGT causes autolysis, and five autolysis sites, R21, R32, K122, R153, and R201, were identified from its autolysate. RESULTS: The tbcf (K101A, R201V) mutant was screened by a directed selection approach for improved activity in flask culture (60.85 ± 3.42 U mL-1, increased 1.5-fold). From the molecular dynamics simulation, in the K101A/R201V mutant the distance between the catalytical residues D102 and H57 was shortened to 6.5 Å vs 7.0 Å in the wild type, which afforded the improved specific activity of 1527.96 ± 62.81 U mg-1. Furthermore, the production of trypsin was increased by 302.8% (689.47 ± 6.78 U mL-1) in a 3-L bioreactor, with co-overexpression of chaperones SSO2 and UBC1 in Pichia pastoris. CONCLUSIONS: SGT protein could be a good source of trypsin for insulin production. As a result of the hydrolysates analysis and direct selection, the activity of the tbcf (K101A, R201V) mutant increased 1.5-fold. Furthermore, the production of trypsin was improved threefold by overexpressing chaperone protein in Pichia pastoris. Future studies should investigate the application of SGT to insulin and pharmaceutical manufacturing.

High-level constitutive expression of leech hyaluronidase with combined strategies in recombinant Pichia pastoris.

Hyaluronidases that break down hyaluronan are widely used for preparation of low molecular weight hyaluronan. Leech hyaluronidase (LHyal) is a newly discovered hyaluronidase with outstanding enzymatic properties. The Pichia pastoris expression system of LHyal that depends on AOX1 promoter (PAOX1) has been constructed. However, the addition of the toxic inducer methanol is a big safety concern. Here, a combinational strategy was adopted for constitutive expression of LHyal to high level in P. pastoris. By optimizing the combination of promoters PGAP, PGAP(m), and PTEF1 and signal peptides α-factor, nsB, and sp23, the enzyme activity of extracellular LHyal reached 1.38 × 105 U/mL in shake flasks. N-terminal engineering with neutral polar amino acids further increased LHyal activity to 2.06 × 105 U/mL. In addition, the impact of overexpressing transcription factors Aft1, Gal4-like, and Yap1 on LHyal production was also investigated. We found the co-expression of Aft1 significantly enhanced the expression of LHyal to 3.03 × 105 U/mL. Finally, LHyal activity of 2.12 × 106 U/mL was achieved in a 3-L fermenter, with a high productivity of 1.96 × 104 U/mL/h. The engineered LHyal-producing Pichia pastoris strains will be more attractive for production of hyaluronidase on industrial scale.

Applying the estimand and target trial frameworks to external control analyses using observational data: a case study in the solid tumor setting.

Introduction: In causal inference, the correct formulation of the scientific question of interest is a crucial step. The purpose of this study was to apply causal inference principles to external control analysis using observational data and illustrate the process to define the estimand attributes. Methods: This study compared long-term survival outcomes of a pooled set of three previously reported randomized phase 3 trials studying patients with metastatic non-small cell lung cancer receiving front-line chemotherapy and similar patients treated with front-line chemotherapy as part of routine clinical care. Causal inference frameworks were applied to define the estimand aligned with the research question and select the estimator to estimate the estimand of interest. Results: The estimand attributes of the ideal trial were defined using the estimand framework. The target trial framework was used to address specific issues in defining the estimand attributes using observational data from a nationwide electronic health record-derived de-identified database. The two frameworks combined allow to clearly define the estimand and the aligned estimator while accounting for key baseline confounders, index date, and receipt of subsequent therapies. The hazard ratio estimate (point estimate with 95% confidence interval) comparing the randomized clinical trial pooled control arm with the external control was close to 1, which is indicative of similar survival between the two arms. Discussion: The proposed combined framework provides clarity on the causal contrast of interest and the estimator to adopt, and thus facilitates design and interpretation of the analyses.

Emulating Randomized Controlled Trials with Hybrid Control Arms in Oncology: A Case Study.

This proof-of-concept study retrospectively assessed the feasibility of applying a hybrid control arm design to a completed phase III randomized controlled trial (RCT; CheckMate-057) in advanced non-small cell lung cancer using a real-world data (RWD) source. The emulated trial consists of an experimental arm (patients from the RCT experimental cohort) and a hybrid control arm (patients from the RCT and RWD control cohorts). For the RWD control cohort, this study used a nationwide electronic health record-derived de-identified database. Three frequentist statistical borrowing methods were evaluated: a two-step Cox model, a fixed Cox model, and propensity score-integrated composite likelihood ("Methods 1-3"). The experimental treatment effect for hybrid control designs were evaluated using hazard ratios (HRs) with 95% confidence interval (CI) estimated from the Cox models accounting for covariate differences. The reduction in study duration compared to the RCT was also evaluated. All three statistical borrowing methods achieved comparable experimental treatment effects to that observed in the CheckMate-057 clinical trial, with HRs of 0.73 (95% CI: 0.59, 0.92), 0.74 (95% CI: 0.61, 0.91), 0.72 (95% CI: 0.59, 0.88) for Methods 1-3, respectively. Reduction in study duration time was 99-115 days when borrowing 30-38 events for Methods 1-3, respectively. This study demonstrated that it is feasible to emulate an RCT using a hybrid control arm design using three frequentist propensity-score based statistical borrowing methods. Selection of an appropriate, fit-for-use RWD cohort is critical to minimizing bias in experimental treatment effect.

Durable mechanical circulatory support device use in the United States by geographic region and minority status.

BACKGROUND: Durable mechanical circulatory support device (MCSD) therapy has experienced rapid dissemination in the United States. Few studies have evaluated geographic patterns of its dissemination based upon patient characteristics that could identify potential variation in its application. METHODS: A combined Interagency Registry for Mechanically Assisted Circulatory Support and Medicare dataset identified durable MCSD implants from 2008 through 2014. MCSD implant rates were estimated using yearly US Census population data, estimated from the Centers for Disease Control and Prevention Wide-ranging Online Data for Epidemiologic Research database and stratified by age, race, and United Network for Organ Sharing (UNOS) region. RESULTS: Overall, 16,331 patients received an MCSD implant from 232 unique centers. Annual MCSD implant rate (per 1 million population) significantly increased in each UNOS region (absolute range of increase, 5.3-16.4) with UNOS Region 7 demonstrating the highest overall absolute rate (20.9) in 2014 and UNOS Region 11 demonstrating the greatest relative increase in rate (430.5%). Geographical differences in the rate of MCSD implants were observed among whites and minorities with higher rates of MCSD implants observed for minorities for nearly all UNOS regions across all years. Significantly greater relative increases in MCSD implants for minorities compared with whites were observed within UNOS Regions 2, 3, 6, 7, 8, 9, and 11 (P < .001). CONCLUSIONS: Geographical differences exist in rates of MCSD implantation among whites and minorities. The reasons for these differences are unknown, but may reflect underlying differences in disease burden or disparities in access to heart transplantation and warrant further study.

[Optimization of enterokinase secretion in Pichia pastoris].

Enterokinase is a class of serine proteases that specifically recognize the cleavage DDDDK sequences. Therefore, enterokinase has been widely used as a tool enzyme in the field of biomedicine. Currently, the expression level of enterokinase in Pichia pastoris is low, which hinders related practical applications. In this study, the effects of six different signal peptides SP1, SP2, SP3, SP4, SP7 and SP8 on the secretory expression of enterokinase in Pichia pastoris were studied. Compared with α-factor, SP1 significantly increased the secretory expression of enterokinase (from 6.8 mg/L to 14.3 mg/L), and the enterokinase activity increased from (2 390±212) U/mL to (4 995±378) U/mL in shaking flask cultures. On this basis, the enterokinase activity was further enhanced to (7 219±489) U/mL by co-expressing the endogenous protein Kex2. Moreover, the activity that the mutant strain with N-terminal fusion of three amino acids of WLR was increased to (15 145±920) U/mL with a high specific activity of (1 174 600±53 100) U/mg. The efficient secretory expression of enterokinase laid a foundation for its applications in near future.

Center Variation in Medicare Spending for Durable Left Ventricular Assist Device Implant Hospitalizations.

Importance: Hospitalizations for durable left ventricular assist device (LVAD) implants are expensive and increasingly common. Insights into center-level variation in Medicare spending for these hospitalizations are needed to inform value improvement efforts. Objective: To examine center-level variation in Medicare spending for durable LVAD implant hospitalizations and its association with clinical outcomes. Design, Setting, and Participants: Retrospective cohort study of linked Medicare administrative claims and Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) clinical data comprising 106 centers in the United States providing durable LVAD implant. Centers were grouped into quartiles based on the mean price-standardized Medicare spending of their patients. The study included Medicare beneficiaries receiving primary durable LVAD implant between January 2008 and December 2014. Data were analyzed between November 2017 and October 2018. Main Outcomes and Measures: Price-standardized Medicare payments and clinical outcomes. Overall and component (facility diagnosis-related group payments, outlier payments, physician services) payments and clinical outcomes (postimplant length of stay and adverse events) were compared across payment quartiles. Results: The study sample included 4442 hospitalized patients, with mean (SD) age of 63.0 (10.8) years, 18.7% female, 27.2% nonwhite, and 6.1% Hispanic ethnicity. Among 4442 hospitalizations, the mean (SD) price-standardized Medicare payment was $176 825 ($60 286) and ranged from $122 953 to $271 472 across 106 centers. The difference in price-standardized payments between lowest and highest spending quartiles was $55 446 ($152 714 vs $208 160; 36%; P < .001), with outlier payments making up most of the difference ($42 742; 77%), followed by DRG ($6929; 13%) and physician services ($5774; 10%). After risk standardization, there was a modest decline in the difference in payments between quartiles ($53 221; 35%), with outlier payments accounting for a larger proportion of the difference (84%). After adjusting for patient characteristics, higher price-standardized payment quartiles were associated with longer postimplant length of stay but were not associated with any adverse events. Conclusions and Relevance: Medicare payments for durable LVAD implant hospitalizations vary widely across centers; this was not well explained by prices or case mix. While associated with longer postimplant length of stay, increased spending was not associated with adverse events. As the supply and demand for durable LVAD therapy continues to rise, identifying opportunities to reduce variation in spending from both explained and unexplained sources will ensure high-value use.

Molecular Engineering of Bacillus paralicheniformis Acid Urease To Degrade Urea and Ethyl Carbamate in Model Chinese Rice Wine.

Bacillus paralicheniformis urease (BpUrease) has been shown to be a promising biocatalyst for degrading the carcinogenic chemical ethyl carbamate (EC or urethane) in rice wine. However, low EC affinity and catalytic efficiency limit the practical application of BpUrease. In this study, we improved the EC degradation capability of BpUrease by site-saturation mutagenesis (SSM). The best variant L253P/L287N showed a 49% increase in EC affinity, 1027% increase in catalytic efficiency ( kcat/ Km), and 583% increase in half-life ( t1/2) at 70 °C. Homology modeling analysis suggest that mutation of Leu253 to Pro increased the BpUrease EC specificity by affecting the interaction between Arg339 with the catalytic residue His323, while Leu287Asn mutation benefits EC specificity and affinity by changing the interaction networks among the residues in the catalytic pocket. Our results show that the L253P/L287N variant efficiently degraded urea and EC in a model rice wine, making it a good candidate for practical application in the food industry.

Linkage of Medicare Records to the Interagency Registry of Mechanically Assisted Circulatory Support.

BACKGROUND: The Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) is a United States registry for adults receiving durable United States Food and Drug Administration-approved mechanical circulatory support devices (MCSDs). We merged INTERMACS records with Medicare claims to investigate the uncertainty of penetrance of Medicare beneficiaries within INTERMACS. METHODS: INTERMACS records and Medicare claims (January 1, 2008, through December 31, 2013) from the Centers for Medicare and Medicaid (CMS) were linked using a deterministic matching methodology. RESULTS: There was annual growth of CMS and INTERMACS centers performing durable MCSD implants among adults from 2008 through 2013 (54% and 87% increase, respectively). The number of CMS centers outnumbered INTERMACS centers throughout all years, with the 68% to 88% of CMS centers being represented in INTERMACS. Although annual patient volume was greatest for INTERMACS, the absolute number of patients significantly increased annually across both data sets from 2008 through 2013 (149% increase in CMS; 268% increase in INTERMACS). As a proportion of all INTERMACS registrants, Medicare beneficiary representation grew from 30% in 2008 to a high of 48% in 2010 and remained stable thereafter. Representation within INTERMACS of MCSDs implanted in Medicare beneficiaries more than doubled, from 36% in 2008 to 77% in 2013. CONCLUSIONS: Using a merged data set of MCSDs implanted between 2008 and 2013, we report that the vast majority of CMS centers and Medicare beneficiaries receiving MCSDs are increasingly captured in INTERMACS. Accordingly, contemporary studies in INTERMACS are relevant and generalizable to the Medicare population.

A roadmap for evaluating the use and value of durable ventricular assist device therapy.

Heart failure is a disease characterized by profound human suffering with limitations in survival despite treatment with guideline-directed medical therapies. Patients with heart failure frequently progress to advanced stages and often require cardiac transplantation or implantation of left ventricular assist devices (LVADs) to extend survival and improve quality of life. As the number of suitable heart donors, number of experienced medical centers and patient comorbidities place restrictions on the feasibility of cardiac transplantation, implantation of LVADs has emerged as a more frequently applied treatment as either a bridge to transplantation or as permanent therapy. Considerable data have documented improvements in survival, functional status and quality of life offered by LVADs, however, few studies have focused on identifying: (1) determinants of LVAD use across medical centers, (2) the relationship between the determinants of LVAD use and value (defined as quality divided by cost), and (3) how determinants of LVAD use are influenced or impacted by vulnerable populations. We propose a conceptual model that integrates the main determinants of LVAD utilization, which include technology, insurance coverage, market-, provider- and patient-level factors. We propose this paradigm as a necessary prerequisite for understanding LVAD usage and value. This conceptual framework provides a broader view for future studies, which are needed to inform emerging healthcare policies that influence dissemination of this expensive but life-prolonging medical therapy.

A Preoperative Risk Model for Postoperative Pneumonia After Coronary Artery Bypass Grafting.

BACKGROUND: Postoperative pneumonia is the most prevalent of all hospital-acquired infections after isolated coronary artery bypass graft surgery (CABG). Accurate prediction of a patient's risk of this morbid complication is hindered by its low relative incidence. In an effort to support clinical decision making and quality improvement, we developed a preoperative prediction model for postoperative pneumonia after CABG. METHODS: We undertook an observational study of 16,084 patients undergoing CABG between the third quarter of 2011 and the second quarter of 2014 across 33 institutions participating in the Michigan Society of Thoracic and Cardiovascular Surgeons Quality Collaborative. Variables related to patient demographics, medical history, admission status, comorbid disease, cardiac anatomy, and the institution performing the procedure were investigated. Logistic regression through forward stepwise selection (p < 0.05 threshold) was utilized to develop a risk prediction model for estimating the occurrence of pneumonia. Traditional methods were used to assess the model's performance. RESULTS: Postoperative pneumonia occurred in 3.30% of patients. Multivariable analysis identified 17 preoperative factors, including demographics, laboratory values, comorbid disease, pulmonary and cardiac function, and operative status. The final model significantly predicted the occurrence of pneumonia, and performed well (C-statistic: 0.74). These findings were confirmed through sensitivity analyses by center and clinically important subgroups. CONCLUSIONS: We identified 17 readily obtainable preoperative variables associated with postoperative pneumonia. This model may be used to provide individualized risk estimation and to identify opportunities to reduce a patient's preoperative risk of pneumonia through prehabilitation.

Heterogeneity of The CD90+ Population in Different Stages of Hepatocarcinogenesis.

We have characterized herein the heterogeneity of the CD90+ population at each stage of hepatocarcinogenesis using a computer-assisted immunohistochemical staining evaluation method for quantitative analysis on tissue microarrays. We found that CD90 in Hepatocellular carcinoma (HCC) tissues, which has been shown to be a marker for cancer stem cells, is expressed on tumor cells, in the stroma or on endothelial cells. Sub-classification of the CD90+ population was based on morphology and co-expression with known markers including CD45 and CD31. Multiple linear regression suggested that the percentage of CD90+ cancer cells/hepatocyte (p<0.0001), level of overall CD90 expression (p<0.0014), and level of CD90 expression in tumor islands (p<0.0001) increased significantly in each stage of liver disease progression, while the level of stromal CD90 expression (p=0.1129) did not change significantly. Additionally, only the CD90+ cancer cells were positive for other cancer stem cell (CSC) markers including CD24, CD44 and CD133 whereas the other CD90+ cells were negative for these markers. CD90 expression in cirrhosis was observed in hepatocytes, the portal tract area and fibrous septa while CD90 expression in normal liver was limited only to the portal tract area. This study demonstrates the heterogeneity of the CD90+ population in HCC where a small population of the CD90+ cells that expressed other CSC markers are CSCs and are associated with advanced stages of hepatocarcinogenesis. This heterogeneity should be emphasized in further studies where other methods may not be able to discriminate these distinct types of CD90+ cells.