Seolhyun Lee, MD

All Publications

• Association of obstructive sleep apnea and diurnal variation of cystatin C. BMC nephrology Lee, S., Noh, S., Lee, W. H. 2024; 25 (1): 40

  Abstract

  Obstructive sleep apnea is a known risk factor for the progression of chronic kidney disease. To find early signs of the progression in subjects with obstructive sleep apnea., we assessed the diurnal variation of kidney biomarkers.A prospective observational study was conducted at Kangwon National University Hospital, Chuncheon, South Korea. All participants underwent in-laboratory polysomnography and phlebotomy in the evening before the polysomnography and in the morning after the polysomnography. Kidney biomarkers, including serum creatinine, blood urea nitrogen, and serum cystatin C, were measured. Delta kidney biomarkers were calculated by subtracting the evening level of the biomarkers from the morning level.Twenty-six of 50 participants had severe obstructive sleep apnea. Delta cystatin C was significantly correlated with apnea-hypopnea index, oxygen desaturation index, and total arousal index with coefficients of -0.314, -0.323, and -0.289, respectively. In participants without severe obstructive sleep apnea, the morning cystatin C level (0.84 ± 0.11 mg/L) was significantly higher than the evening cystatin C level (0.81 ± 0.11 mg/L) (P = 0.005). With severe obstructive sleep apnea, the cystatin C levels were not different between the morning (0.85 ± 0.11 mg/L) and the evening (0.85 ± 0.10 mg/L).Cystatin C level was increased in the morning in participants without severe obstructive sleep apnea, but not in participants with severe obstructive sleep apnea.

  View details for DOI 10.1186/s12882-024-03472-7

  View details for PubMedID 38287274

  View details for PubMedCentralID 2975904

• Increasing the Clearance of Protein Bound Solutes by Recirculating Dialysate through Activated Carbon. Kidney360 Meyer, T. W., Lee, S., Whitmer, L. C., Blanco, I. J., Suba, J. K., Sirich, T. L. 2023

  Abstract

  BACKGROUND: Conventional hemodialysis provides limited clearance of uremic solutes that bind to plasma proteins. No studies however have tested testing whether increasing the clearance of bound solutes provides clinical benefit. Practical means to increase the dialytic clearance of bound solutes are required to perform such studies.METHODS: Artificial plasma was dialyzed using two dialysis systems in series. In the first recirculating system a fixed small volume of dialysate flowed rapidly through an activated carbon block before passing through two large dialyzers. In a second conventional system a lower flow of fresh dialysate was passed through a single dialyzer. Chemical measurements tested the ability of the recirculating system to increase the clearance of selected solutes. Mathematical modeling predicted the dependence of solute clearances on the extent to which solutes were taken up by the carbon block and were bound to plasma proteins.RESULTS: By itself, the conventional system provided clearances of the tightly bound solutes p-cresol sulfate (PCS) and indoxyl sulfate (IS) of only 18±10 and 19±11 ml/min, respectively (mean±sd). Because these solutes were effectively adsorbed by the carbon block, the recirculating system by itself provided PCS and IS clearances of 45±11 and 53±16 ml/min. It further raised their clearances to 54±12 ml/min and 61±17 ml/min when operating in series with the conventional system (p < 0.002 vs conventional clearance both solutes). Modeling predicted that the recirculating system would increase the clearances of bound solute even if their uptake by the carbon block was incomplete.CONCLUSIONS: When added to a conventional dialysis system, a recirculating system employing a carbon block sorbent, a single pump, and standard dialyzers can greatly increase the clearance of protein-bound uremic solutes.

  View details for DOI 10.34067/KID.0000000000000155

  View details for PubMedID 37211642

• Removal of Uremic Solutes from Dialysate by Activated Carbon. Clinical journal of the American Society of Nephrology : CJASN Lee, S., Sirich, T. L., Blanco, I. J., Plummer, N. S., Meyer, T. W. 2022

  Abstract

  BACKGROUND AND OBJECTIVES: Adsorption of uremic solutes to activated carbon provides a potential means to limit dialysate volumes required for new dialysis systems. The ability of activated carbon to take up uremic solutes has, however, not been adequately assessed.DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Graded volumes of waste dialysate collected from clinical hemodialysis treatments were passed through activated carbon blocks. Metabolomic analysis assessed the adsorption by activated carbon of a wide range of uremic solutes. Additional experiments tested the ability of the activated carbon to increase the clearance of selected solutes at low dialysate flow rates.RESULTS: Activated carbon initially adsorbed the majority, but not all, of 264 uremic solutes examined. Solute adsorption fell, however, as increasing volumes of dialysate were processed. Moreover, activated carbon added some uremic solutes to the dialysate, including methylguanidine. Activated carbon was particularly effective in adsorbing uremic solutes that bind to plasma proteins. In vitro dialysis experiments showed that introduction of activated carbon into the dialysate stream increased the clearance of the protein-bound solutes indoxyl sulfate and p-cresol sulfate by 77%±12% (mean±SD) and 73%±12%, respectively, at a dialysate flow rate of 200 ml/min, but had a much lesser effect on the clearance of the unbound solute phenylacetylglutamine.CONCLUSIONS: Activated carbon adsorbs many but not all uremic solutes. Introduction of activated carbon into the dialysate stream increased the clearance of those solutes that it does adsorb.

  View details for DOI 10.2215/CJN.01610222

  View details for PubMedID 35835518

• Improving Solute Clearances by Hemodialysis. Blood purification Lee, S., Sirich, T. L., Meyer, T. W. 2022: 1-12

  Abstract

  The adequacy of hemodialysis is now assessed by measuring the removal of the single-solute urea. The urea clearance provided by contemporary dialysis is a large fraction of the blood flow through the dialyzer and therefore cannot be increased much further. Other solutes however likely contribute more than urea to the residual uremic illness suffered by hemodialysis patients. We here review methods which could be employed to increase the clearance of nonurea solutes. We will separately consider the clearances of free low-molecular-mass solutes, free larger solutes, and protein-bound solutes. New clinical studies will be required to test the extent to which increasing the clearance on nonurea solutes with these various characteristics can improve patients' health.

  View details for DOI 10.1159/000524512

  View details for PubMedID 35613554

• Impaired Tubular Secretion of Organic Solutes in Advanced CKD. Journal of the American Society of Nephrology : JASN Mair, R., Lee, S., Plummer, N., Sirich, T., Meyer, T. 2021

  Abstract

  Background The clearance of solutes removed by tubular secretion may be altered out of proportion to the glomerular filtration rate (GFR) in chronic kidney disease (CKD). Recent studies have described considerable variability in the secretory clearance of waste solutes relative to the GFR in patients with CKD. Methods To test the hypothesis that secretory clearance relative to GFR is reduced in patients approaching dialysis, we used metabolomic analysis to identify solutes in simultaneous urine and plasma samples from 16 CKD patients with an estimated GFR of 7±2 ml/min per 1.73m2 and 16 control participants. Fractional clearances were calculated as the ratios of urine to plasma levels of each solute relative to those of creatinine and urea in CKD patients and to those of creatinine in controls. Results Metabolomic analysis identified 39 secreted solutes with fractional clearance >3.0 in control participants. Fractional clearance values in CKD patients were reduced on average to 65%±27% of those in controls. These values were significantly lower for 18 of 39 individual solutes and significantly higher for only one. Assays of the secreted anions phenylacetyl glutamine, p-cresol sulfate, indoxyl sulfate, and hippurate confirmed variable impairment of secretory clearances in advanced CKD. Fractional clearances were markedly reduced for phenylacetylglutamine (4.2±0.6 for controls versus 2.3±0.6 for CKD patients, P<0.001), p-cresol sulfate (8.6±2.6 for controls versus 4.1±1.5 for CKD patients, P<0.001), and indoxyl sulfate (23.0±7.3 versus 7.5±2.8, P<0.001), but not for hippurate (10.2±3.8 versus 8.4±2.6, P=0.13). Conclusions Secretory clearances for many solutes are reduced more relative to the reduction in GFR in advanced CKD. Impaired secretion of these solutes might contribute to uremic symptoms as patients approach dialysis.

  View details for DOI 10.1681/ASN.2021030336

  View details for PubMedID 34408065

• Improving Clearance for Renal Replacement Therapy. Kidney360 Lee, S., Sirich, T. L., Meyer, T. W. 2021; 2 (7): 1188-1195

  Abstract

  The adequacy of hemodialysis is now assessed by measuring the removal of a single solute, urea. The urea clearance provided by current dialysis methods is a large fraction of the blood flow through the dialyzer, and, therefore, cannot be increased much further. However, other solutes, which are less effectively cleared than urea, may contribute more to the residual uremic illness suffered by patients on hemodialysis. Here, we review a variety of methods that could be used to increase the clearance of such nonurea solutes. New clinical studies will be required to test the extent to which increasing solute clearances improves patients' health.

  View details for DOI 10.34067/kid.0002922021

  View details for PubMedID 35355887

  View details for PubMedCentralID PMC8786098