Abstract

Background/Aims: We evaluated the biocompatibility of the new dialyzer TORAYLIGHT^® NV, which was developed by focusing on the mobility of water adjacent to the membrane surface.
In the TORAYLIGHT^® NV, the mobility of water adjacent to the membrane surface was enhanced by using a new hydrophilic polymer to reform the membrane surface.
Methods: The TORAYLIGHT^® NV was used in 6 maintenance dialysis patients 3 times a week for 2 weeks. Next, the conventional dialyzer TORAYLIGHT^® CX was used in the same patients 3 times a week for 2 weeks. We evaluated the variability in several parameters including the white blood cell and platelet counts as indexes for biocompatibility.
Results: Platelet activation and the number of platelets adhering to the membrane surface were lower with the TORAYLIGHT^® NV than with the TORAYLIGHT^® CX. The variability of hematocrit was also lower with the TORAYLIGHT^® NV than with the TORAYLIGHT^® CX.
Conclusion: Our data suggest that the TORAYLIGHT^® NV has good biocompatibility and can potentially enhance plasma refilling during dialysis.

Keywords biocompatibility, TORAYLIGHT^® NV, thrombocytopenia, plasma refilling rate, PRR, hemodialyzer, hemodialysis

Author and Article Information

Author info
1) Division of Clinical Engineering, Japan Community Healthcare Organization Tokyo Yamate Medical Center
2) Division of Nephrology, Japan Community Healthcare Organization Tokyo Yamate Medical Center

RecievedMar 31 2014　　AcceptedMay 2 2014　　PublishedMay 14 2014

CitationYamaka T, Ichikawa K, Saito M, Watanabe K, Nakai A, Higuchi N, Igarashi N, Yoshimoto H (2014) Biocompatibility of the new anticoagulant dialyzer TORAYLIGHT^® NV. Science Postprint 1(1): e00020. doi: 10.14340/spp.2014.05C0002

Copyright©2014 The Authors. Science Postprint is published by General Healthcare Inc. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs 2.1 Japan (CC BY-NC-ND 2.1 JP) License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

FundingToray Medical Co., Ltd provided funds for the laboratory diagnostic tests performed in this study. The funder had no role in study design, collection, analysis, and interpretation of data, the decision to publish, or the preparation of the manuscript.

Competing interestThe authors have no relevant competing interests to disclose.

Ethics statementThis study was conducted in accordance with the guidelines of the Declaration of Helsinki and approved by the ethics committee of Social Insurance Chuo General Hospital. We obtained written informed consent from all participants.

Corresponding authorYamaka Toshihiko
AddressDivision of Clinical Engineering, Japan Community Healthcare Organization Tokyo Yamate medical Center,
Hyakunin-cho 3-22-1, shinjukuku, Tokyo 169-0073, Japan
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Introduction

The three available therapies for end-stage renal disease (ESRD) are hemodialysis (HD), continuous ambulatory peritoneal dialysis, and kidney transplantation. Among these, HD is most commonly administered to ESRD patients in most countries 1. Currently, a hemodialyzer that consists of hollow fiber membranes is widely used in HD.
Complications are frequently observed in HD patients, which are considered related to the so-called bioincompatibility. Such bioincompatibilities include leukopenia 2, compliment activation 3, 4, and thrombocytopenia 5-7, and are believed to be induced by the interaction between the membrane material and blood components such as blood cells 4, 8. To avoid bioincompatibilities, numerous manufacturers currently produce hemodialyzers using a variety of polymers and improved manufacturing processes, resulting in the development of biocompatible dialyzers.
The condition of the water adjacent to the material surface is reportedly related to the material’s biocompatibility 9-11. The TORAYLIGHT^® NV (NV) is a dialyzer that was developed by focusing on the mobility of water adjacent to the membrane surface 12. In the NV, the mobility of water adjacent to the membrane surface is enhanced by using a new hydrophilic polymer to reform the membrane surface. Furthermore, the presence of a uniform and thick hydrophilic layer on the surface of the hollow fiber membrane NV was confirmed by attenuated total reflection-infrared (ATR-IR) spectroscopy 12.
In this study, we compared the biocompatibilities of the NV with those of the TORAYLIGHT^® CX (CX), the membrane surface of which has not been reformed with the novel hydrophilic polymer. Platelet activation and the number of platelets adhering to the membrane surface were lower with the NV than with the CX. We were therefore able to confirm that the NV has good biocompatibilities.

Methods

Dialyzer

In this study, the TORAYLIGHT^® NV (Toray Industries, Inc., Tokyo, Japan) was the study object and was compared with the TORAYLIGHT^® CX (Toray Industries, Inc., Tokyo, Japan). The same polysulfone-based membrane is used in both the NV and the CX, but the membrane surface of the NV is reformed using polyvinylpyrrolidone and a new hydrophilic polymer 12. In this study, we used dialyzers with an effective surface area of l.6 m².

Study design

Six stable chronic maintenance dialysis patients who were receiving dialysis for 4 h 3 times a week were enrolled. The blood flow rate was 200 mL/min and the dialysate flow rate was 500 mL/min. The NV was used in these patients 3 times a week for 2 weeks, followed by the CX 3 times a week for 2 weeks. Blood samples and used dialyzers were collected at the first dialysis session of each second week. Blood samples were collected at the beginning of dialysis and after 15, 60, and 240 min. Blood cell counts were measured using an automatic hemocytometer. Platelet factor-4 (PF-4) and β-thromboglobulin (β-TG) concentrations were measured using an enzyme immunoassay (EIA). The membrane surfaces of the collected dialyzers were analyzed by Scanning Electron Microscope. This study was conducted in accordance with the guidelines of the Declaration of Helsinki and approved by the ethics committee of Social Insurance Chuo General Hospital. We obtained written informed consent from all participants.

Variability of platelet, white blood cell (WBC), and hematocrit (Hct) counts during dialysis

Platelet, WBC, and Hct counts were measured at the beginning of dialysis and after 15, 60, and 240 min. To compensate for differences in cell counts at the beginning of dialysis, we calculated the change ratio at each point using the following formula (I).

Change ratio _Xmin =100 × {(Cell count _Xmin)/(Cell count _0min) − 1} (I)
Cell count _0min: Cell count at the beginning of dialysis
Cell count _Xmin: Cell count after X minutes from the beginning of dialysis

Variability of platelet activation marker concentrations during dialysis

Blood concentrations of PF-4 and β-TG were measured at the beginning of dialysis and after 15, 60, and 240 min using an EIA. Then, on the assumption that each value measured before dialysis was 100%, the results were evaluated for variability.

Analysis of matter adhering to the hollow fiber membranes

We collected the dialyzers used in the dialysis treatment and infused them with saline to remove residual blood. The dialyzers were then filled with 3% glutaraldehyde for sterilization and fixation of blood components adhering to the membrane surface. The dialyzers were disassembled, and hollow fibers were collected. Hollow fibers were cut in the major axis direction and the inner surface was observed with a SEM.

Statistics

Data were evaluated using paired t-tests. Significant differences were noted at P <0.05.

Results

Variability in platelet and white blood cell counts during dialysis

The variability in the platelet count during HD is shown in Figure 1. With the NV, the platelet count hardly changed during the hemodialysis session. However, with the CX, the platelet count decreased after the start of HD. In particular, the platelet count 15 min after the start of HD was significantly lower with the CX than with the NV (Figure 1A). The change ratios after 15 and 60 min were significantly lower with the CX than with the NV (Figure 1B). There were no differences in the variability of the WBC count between the NV and CX, even after calculating the change ratio (Figure 2).

Figure 1Variability in platelet count during hemodialysis with the TORAYLIGHT^® NV and CX

A: Change in platelet count during hemodialysis, B: Change ratio of platelets during hemodialysis. Results are presented as mean ± standard deviation (n = 6). *: P <0.05

Figure 2Variability in white blood cell count during hemodialysis with the TORAYLIGHT^® NV and CX

A: Change in white blood cell count during hemodialysis, B: Change ratio of white blood cells during hemodialysis. Results are presented as mean ± standard deviation (n = 6). There were no significant differences between the two dialyzers.

Variability in Hct count during dialysis

Figure 3 shows the variability of Hct count during dialysis. Hct count increased after dialysis with both the CX and NV. The volume of removed water did not differ significantly between treatment using the NV and treatment using the CX (NV and CX: 2.34 ± 0.30 L/session and 2.59 ± 0.40 L/session, respectively, P = 0.11). There was a significant difference between the two groups after 60 and 240 min, and the variability was lower with the NV (Figure 3).

Figure 3Change ratio of hematocrit during hemodialysis with the TORAYLIGHT^®　NV and CX

Results are presented as mean ± standard deviation (n = 6). *: p<0.05, **: p<0.01

Variability in platelet activation marker levels during dialysis

It is well known that both PF-4 and β-TG are platelet activation markers. The variability in the PF-4 and β-TG levels in each case during dialysis is shown in Figure 4. The mean variability in the levels of these markers did not significantly differ between the two groups, but the distributions of PF-4 and β-TG were smaller with the NV than with the CX.

Figure 4Comparison of the variability in platelet factor-4 (PF-4) and β-thromboglobulin (β-TG) levels during hemodialysis with the TORAYLIGHT^®　NV and CX

A: Variability in PF-4 level during hemodialysis with the NV, B: Variability in PF-4 level during hemodialysis with the CX, C: Variability in β-TG level during hemodialysis with the NV, D: Variability in β-TG level during hemodialysis with the CX. Results are presented as means or individual patients (n = 6).

Analysis of matter adhering to the hollow fiber membranes

After the use of each dialyzer, the inner surfaces of the hollow fiber membranes were examined by SEM (Figure 5). We could observe platelets adhering to the inner membrane surface in 5 of the 6 cases with the CX, but could confirm platelets in only one case with the NV. The conditions regarding Hct changes on six patients were shown in Table 1.

Figure 5Comparison of hollow fiber membrane surfaces of dialyzers after use

The inner surfaces of hollow fiber membranes were observed with a Scanning Electron Microscope (SEM). The pictures obtained from 6 patients are presented.

Table 1The condition regarding Hct changes on six patients

Discussion

The NV is a dialyzer that was developed by focusing on the mobility of water adjacent to the membrane surface, which was enhanced by using a new hydrophilic polymer to reform the membrane surface 12. While we did not compare the removal performance of small molecular weight substances using the NV with that of the CX, there were no differences between the two dialyzers in this regard.
To evaluate the biocompatibility of the NV, we compared the variability of several parameters such as platelet, WBC, and Hct counts during dialysis. The variability in the WBC count was not different between the NV and CX, but the variability in the platelet count was stable without much fluctuation with the NV compared to that with the CX (Figure1 and 2). Furthermore, the platelet activation marker PF-4 and β-TG levels showed similar tendencies in all 6 cases (Figure 4). We consider that these findings are responsible for the drastic reduction in platelet adhesion to the inner surfaces of the hollow fiber membranes after dialysis (Figure 5). When we focus on the platelet and WBC counts before dialysis, we observe that the WBC count did not differ between the two dialyzers, but the platelet count was higher with the NV than with the CX, although there were no significant differences. This phenomenon might indicate that the low platelet activation by NV increases the platelet count. Although existing polysulfone membranes occasionally cause thrombocytopenia 5, 13, 14, on the basis of the aforementioned results, we consider that the use of the NV may reduce such risks.
Hct count normally increases after HD because blood components are concentrated by water removal. In this study, the Hct count was significantly lower when the NV was used than when the CX was used, as shown in Figure 3, although there was no significant difference in water removal between the two dialyzers. Water removed from the intravascular space is recovered by the movement of water from the interstitial and intracellular spaces to the intravascular space. This mechanism is known as “plasma refilling,” and clinicians have recently emphasized the importance of this mechanism 15, 16. In the case of a high plasma refilling rate (PRR), the change in the concentration of blood components such as Hct is considered to be low because the change in the volume of water in the intravascular space is low. Our results suggest that the NV can potentially increase PRR compared with a conventional dialyzer. Furthermore, patients with higher plasma refilling show fewer hypotensive episodes because the fluid removed from the intravascular space is promptly replaced by interstitial and intracellular volume 17-21. We expect that hypotension during HD will decrease with the use of the NV as compared to the conventional dialyzer, although we did not measure blood pressure during dialysis with the NV. In actuality, some clinical findings concerning the decrease of hypotension frequency by using the NV have been reported in Japan 22. We expect to conduct a randomized controlled trial in patients who are prone to hypotension.
The numbers of platelets adhering to the membrane surface were found to be lower with the NV than with the CX on analysis of the blood components adhering to the membrane surface of used dialyzers (Figure 5). Ueno et al. reported in vitro results using the model membrane reformed with the new hydrophilic polymer and human whole blood 12. Similar to our results, they observed platelet adhesion on a conventional membrane such as the CX but not on a reformed membrane like the NV. With regard to their in vitro experiment, it seems that water removal and hemoconcentration should not be considered along with the property of the membrane surface because human blood was put on the model membrane and incubated, and their results suggest that low platelet activation by the NV resulted in the reduction of platelet adhesion to the membrane. However, in our study, we think that the contribution of hemoconcentration to our results should be considered because there was a significant difference in Hct count between the two groups despite the absence of a significant difference in water removal.

Conclusions

Platelet activation with the TORAYLIGHT^® NV was lower than that with a conventional dialyzer, and we were able to confirm that the TORAYLIGHT^® NV has good biocompatibilities. In addition, the TORAYLIGHT^® NV can potentially enhance plasma refilling during dialysis.

Acknowledgements

We are grateful to the staff of the Division of Clinical Engineering and Nephrology, Japan Community Healthcare Organization Tokyo Yamate Medical Center, for providing beneficial advice.

Author Contributions

Yamaka T: Conceived and designed the experiments, wrote the paper
Nakai A, Higuchi N, and Igarashi N: Analyzed the data
Ichikawa K, Saito M, and Watanabe K: Acquisition of data
Yoshimoto H: Approved the manuscript

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