ASN's Mission

ASN leads the fight to prevent, treat, and cure kidney diseases throughout the world by educating health professionals and scientists, advancing research and innovation, communicating new knowledge, and advocating for the highest quality care for patients.

learn more

Contact ASN

1401 H St, NW, Ste 900, Washington, DC 20005

email@asn-online.org

202-640-4660

The Latest on Twitter

Kidney Week

Abstract: PO1173

pH-Dependent Protein Binding Properties of Uremic Toxins In Vitro

Session Information

Category: Dialysis

  • 701 Dialysis: Hemodialysis and Frequent Dialysis

Authors

  • Yamamoto, Suguru, Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
  • Sasahara, Kenji, Institute for Protein Research, Osaka University, Osaka, Japan
  • Domon, Mio, Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
  • Yamaguchi, Keiichi, Institute for Protein Research, Osaka University, Osaka, Japan
  • Ito, Toru, Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
  • Goto, Shin, Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
  • Goto, Yuji, Institute for Protein Research, Osaka University, Osaka, Japan
  • Narita, Ichiei, Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
Background

Patients with chronic kidney disease undergoing dialysis treatment have worse clinical outcomes. One cause is the interactions between various uremic toxins and organ/tissues. Protein-bound uremic toxins (PBUTs), such as indoxyl sulfate (IS) and p-cresyl sulfate (PCS), are difficult to remove by conventional dialysis treatment owing to their high protein binding property. A possible treatment strategy is to weaken the protein binding of PBUTs. Acidic and alkaline pH change the conformation of proteins, which may be associated with the binding of uremic toxins. We examined the influence of pH on the protein binding properties of PBUTs in vitro.

Methods

Albumin conformation at pH 2 to 13 was analyzed using circular dichroism. Albumin reacted with IS at pH 4 to 11. The protein binding behavior was examined using isothermal titration calorimetry and free IS concentration was measured by mass spectrometry. Bovine serum with IS, PCS, indole acetic acid (IAA), or phenyl sulfate (PhS), as well as serum from hemodialysis patients, were adjusted to a pH of 4 to 11, and the concentration of the free form of PBUTs was measured.

Results

Albumin partially unfolded at pH <4 or >12. Calorimetric analyses revealed weakened interaction between IS and albumin at pH <5 or >10. The concentration of free IS in the presence of albumin was significantly increased at pH 4 (89.49±1.38 μg/dL) and pH 11 (22.45±1.38 μg/dL) compared to pH 7 (17.20±0.87 μg/dL) (both p<0.01). Addition of bovine serum to IS, PCS, IAA, or PhS at the physiological concentration of uremic patients and adjustment of pH from 4 to 11 resulted in increased concentrations of the free form of the solutes at acidic and alkaline pH, compared with the concentrations at neutral pH. Adjustment of serum from 19 hemodialysis patients from pH 4 to 11 resulted in increased concentrations of the free forms of IS, PCS, PhS, and IAA at acidic and alkaline pH. (e.g., IS: pH 4, 152.5±77.6 μg/dL; pH 11, 153.8±135.5 μg/dL vs pH 8, 38.8±33.4 μg/dL; p<0.01, respectively)

Conclusion

Acidic and alkaline pH changed albumin conformation and weakened protein binding property of PBUTs in vitro. The findings could inform strategies to increase the removal of PBUTs with convection/diffusion in hemodialysis treatment.