The Ratio of Dialysate NGAL to Plasm NGAL (NGAL D/P) Can Reflect Peritoneal Transport in CAPD Patients

Objectives: To probe the role of peritoneal NGAL in reflecting peritoneum function. Methods: 20 CAPD anuria patients without peritonitis in our peritoneal dialysis center were recruited from July 2016 to July 2018. These patients were divided into high-transport peritoneum group and non-high transport peritoneum group according to peritoneal transport type. Patients from both groups received the same dialysis solutions and dialysis modality. Peritoneal transport type, serum C-reactive protein, peritoneal equilibrium test results, dialysate NGAL, plasm NGAL, the ratio of dialysate NGAL to plasm NGAL (D/P NGAL) from both groups were recorded. Spearman’s correlation coefficient was employed to examine the relations between variables. Receiver operating characteristic (ROC) curve analysis was used to calculate the area under the curve (AUC) for ratio of dialysate NGAL to plasm NGAL (D/P NGAL) and peritoneal creatinine to serum creatinine (D/P creatinine). Results: we had recruited 20 patients (11 male and 9 female, 7 high transport and 13 non-high transport group,). D/P NGAL had a correlation with D/P creatinine in CAPD patients (p < 0.05). The area under the ROC curve for D/P NGAL was 0.81. Conclusion: The ratio of dialysate NGAL to plasm NGAL (D/P NGAL) can reflect peritoneal transport in CAPD patients. dialysis (CAPD) patients with anuria without peritonitis to explore whether NGAL could reflect peritoneum function in continuous ambulatory peritoneal dialysis (CAPD) patients.

dialysis (CAPD) patients with anuria without peritonitis to explore whether NGAL could reflect peritoneum function in continuous ambulatory peritoneal dialysis (CAPD) patients.

Patients Selection
Cross-Sectional study. Recruited CAPD patients in our peritoneal dialysis center from July 2016 to July 2018.The design has been approved by the Ethics Committee of the Second affiliated hospital of Wenzhou Medical University. All patients gave their written informed consent before inclusion in the study. Informed consent was obtained from all participants. This study was performed in accordance with the Declaration of Helsinki. Inclusion criteria of this study: aged than 18 years, peritoneal dialysis time more than 90 days, urine volume less than 100 mL/day. Exclusion criteria:

Materials and Methods
Blood samples for plasm NGAL evaluation were collected in chilled vacutainer tubes containing potassium ethylenediaminetetraacetate, and the plasma was promptly analyzed. Plasm NGAL was assayed within 1 hour of sample collection using a Triage NGAL test on a Triage Meter Pro analyzer (Alere, Stockport, UK) on the first day of patients' visit. Long-dwell effluents were collected for dialysate NGAL, WBC count and effluent ten milliliters of peritoneal liquid was centrifuged at 3,000 rpm for 8 minutes and stored at −80°C until assayed. Dialysate NGAL was evaluated in an overnight effluent collection using the Architect platform (Abbott Diagnostics, Abbott Park, IL, USA). The ratio of dialysate NGAL to plasm NGAL (D/P NGAL) was calculated. Plasm NGAL and dialysate NGAL levels were expressed as ng/mL. Demographic data including age, gender, body mass index, major comorbidities at the beginning of PD treatment (diabetes, etc.), biochemical data were also collected in both groups.

Statistical Analysis
Statistical analysis was carried out using SPSS software (Version

Results
The clinical patients' characteristics stratified according to function of peritoneum were reported in Table 1. During the study period, we evaluated 20 patients (7 in the high transport group and 13 in the non-high transport group, 11 male and 9 female). No significant differences were found between two groups in terms of age (p =0.31), gender (p =0.21), comorbidity such as diabetes (p =0.13), dialysis duration (p = 0.31). Significant differences were found between the 2 groups in terms of type of transporter (dialysate to plasma ratio for creatinine, p<0.05), and Kt/V (p<0.05), ultrafiltration volume (p<0.05), also dialysate to plasm ration for NGAL (p <0.05). Analysis of T test showed no significant between two groups in the distribution of peritoneal NGAL and plasm NGAL Showed in Table 1.      The area under the ROC curve for D/P NGAL was 0.81. When the cutoff value of D/P NGAL was set at 0.056, with sensitivity and specificity were 85.7% and 70.0%, respectively. P<0.05.

Discussion
Chronic exposure to PD solutions is associated with impairment of peritoneal host defense. Alterations of cellular components within the peritoneal cavity led to disturbances in the release of pro-inflammatory and anti-inflammatory mediators [6]. NGAL has poor peritoneal diffusive capacity due to large molecular weight (25000 Da) [9]. However, for the first time, we found that the relationship between D/P NGAL and D/P creatinine, which means D/P NGAL can used as a precious marker for peritoneal function. To further explore the role of D/P NGAL in identifying the high transport peritoneum, receiver operating characteristic (ROC) curve analysis was employed. The area under the curve (AUC) for D/P NGAL was 0.81, sensitivity and specificity were 85.7% and 70.0% with the cutoff value of.056 for D/P NGAL, from which we come to the conclusions that D/P NGAL can be used as a reliable marker for high transport peritoneum, as well as D/Pcr and D/D0 glucose.
The relationship between dialysate NGAL and high peritoneal transport peritoneum is very complicated. Peritoneal NGAL may cause peritoneal fibrosis. Chronic exposure to PD solutions is associated with increased small solute transport across the peritoneal membrane and ultrafiltration failure [7]. Particularly, epithelial-to-mesenchymal transition (EMT) of mesothelial cells is often associated with high peritoneal transport [10]. In the state of peritonitis, the transformation of growth factor (TGF-ß), interleukin-1(IL-1) beta can promote reversible EMT [11,12].
Repeated peritonitis is the leading cause of EMT, which may lead to peritoneal fibrosis during CAPD, and finally leading to the termination of PD.
NGAL can impact the process of EMT by regulation of balance between matrix metalloproteinase 9(MMP-9) and tissue inhibitor of metalloproteinase 1 (TIMP-1) [13]. MMP-9, one of the matrix metalloproteinases family, is regulated by NGAL [14].  [15]. However, we did not probe the underlying mechanism in our study due to limited time.
This study certainly had a few limitations. Patient number was slightly limited. This was a single-center Cross-Sectional study with poor generalizability of this study as all the patients were from southern China. To resolve these limitations, a prospective, largescale, multicenter randomized trial is necessary. Also, we did not probe the underlying mechanism behind the correlation between D/P NGAL and D/P creatinine in CAPD patients. Further basal research is needed in future.

Conflict of Interest Statement
We declare that we have no conflicts of interest. All authors made a substantial contribution to the information or material submitted for publication. All read and approved the final manuscript.

Consent For Publication
Written informed consent was obtained from all subjects before the study. See the file of patients' informed consent form.

Availability of Data and Materials
See the file named date and materials.

Ethical Considerations
Ethical issues (Including plagiarism, informed consent,

Funding Sources
Supported by foundation of Wenzhou science and technology Bureau, Y2020971.