Abstract Polyphenol oxidase (PPO) plays a key role in tea processing. It catalyzes the conversion of tea polyphenols into theaflavin and its derivatives. PPO was partially purified and characterized in both its soluble form (sPPO) and membrane-bound form (mPPO) from tea (Camellia sinensis) leaves. Both forms were purified by three-phase partitioning and membrane ultrafiltration. sPPO and mPPO showed high activity against diphenols as substrate and had the highest affinity for catechol and caffeic acid. The optimum temperatures and pH for enzyme activity were different. mPPO was more stable than sPPO in the acidic pH range. Among the chemical inhibitors studied, oxalic acid exerted the highest inhibitory effect on mPPO, whereas EDTA showed the highest inhibitory effect on sPPO. Both sPPO and mPPO showed similar enzymatic synthesis rates in the formation of theaflavin-3'-gallate and theaflavin-3,3'-gallate. At high concentrations of the substrate, the synthesis of theaflavins was inhibited due to the presence of high levels of ester catechins. However, mPPO showed stronger stability against inhibition by ester catechins than sPPO.

Abstract Objective: To discover potentially modifiable perioperative predictors for renal replacement therapy (RRT) in patients with cardiac surgery-associated acute kidney injury (CSA-AKI). Methods: A cohort of 1773 consecutive cardiac surgery patients with postoperative acute kidney injury (AKI) from January 2013 to December 2015 were included retrospectively. AKI was defined according to the Kidney Disease: Improving Global Outcomes (KDIGO) criteria. The primary outcome was CSA-AKI requiring renal replacement therapy (AKI-RRT). The initiation of RRT was based on clinical judgment regarding severe volume overload, metabolic abnormality (e.g., acidosis, hyperkalemia), and oliguria. Patients with AKI-RRT were matched 1:1 with patients without AKI-RRT by a propensity score, to exclude the influence of patients' demographics, comorbidities, and baseline renal function. Multivariable regression was performed to identify the predictors in the matched sample. Results: AKI-RRT occurred in 4.4% of the entire cohort (n=78/1773), with 28.2% of in-hospital mortality (n=22/78). With the propensity score, 78 pairs of patients were matched 1:1 and the variables found to be predictors of AKI-RRT included the contrast exposure within 3 days before surgery (odds ratio [OR]=2.932), central venous pressure (CVP) >10 mmHg on intensive care unit (ICU) admission (OR=1.646 per mmHg increase), and erythrocyte transfusions on the 1st day of surgery (OR=1.742 per unit increase). Conclusion: AKI-RRT is associated with high mortality. The potentially modifiable predictors found in this study require concern and interventions to prevent CSA-AKI patients from worsening prognosis.

Abstract Objective: To assess the clinical value of four models for the prediction of cardiac surgery-associated acute kidney injury (CSA-AKI) and severe AKI which renal replacement therapy was needed (RRT-AKI) in Chinese patients. Methods: 1587 patients who underwent cardiac surgery in the department of cardiac surgery in the Zhongshan Hospital, Fudan University, between January 2013 and December 2013 were enrolled in this research. Evaluating the predicting value for cardiac surgery-associated AKI (AKICS score) and RRT-AKI (Cleveland score, SRI and Mehta score) by Hosmer-Lemeshow goodness-of-fit test for the calibration and area under receiver operating characteristic curve (AUROC) for the discrimination. Results: Based on 2012 KDIGO (Kidney Disease: Improving Global Outcomes) AKI definition, the incidence of AKI and RRT-AKI was 37.4% (594/1587) and 1.1% (18/1587), respectively. The mortality of AKI and RRT-AKI was 6.1% (36/594) and 66.7% (12/18), respectively, while the total mortality was 2.8% (44/1587). The discrimination (AUROC=0.610) for the prediction of CSA-AKI of AKICS was low, while the calibration (x2=7.55, P=0.109) was fair. For the prediction of RRT-AKI, the discrimination of Cleveland score (AUROC=0.684), Mehta score (AUROC=0.708) and SRI (AUROC=0.622) were not good; while the calibration of them were fair (Cleveland score x2=1.918, P=0.166; Mehta score x2=9.209, P=0.238; SRI x2=2.976, P=0.271). Conclusion: In our single-center study, based upon valve surgery dominant and less diabetes mellitus patients, according to KDIGO AKI definition, the predictive value of the four models, combining discrimination and calibration, for respective primary event, were not convincible.