Serum Total p-Cresol and Indoxyl Sulfate Correlated With Stage of Chronic Kidney Disease in Renal Transplant Recipients

Serum Total p-Cresol and Indoxyl Sulfate Correlated With Stage of Chronic Kidney Disease in Renal Transplant Recipients S.-T. Huang, K.-H. Shu, C.-H. Cheng, M.-J. Wu, T.-M. Yu, Y.-W. Chuang, and C.-H. Chen ABSTRACT Background. Uremic toxins are considered cardiovascular and mortality risk factors in chronic kidney disease (CKD) patients. Both p-cresol and indoxyl sulfate have been shown to induce oxidative stress in vitro and subsequent endothelial dysfunction in uremic patients. Our study evaluated the levels of p-cresol and indoxyl sulfate, and whether they contribute to the progression of CKD in transplant recipients. Methods. We retrospectively evaluated 95 patients who had received a transplant from February 1987 to June 2010 in our center; the recipients had a mean transplant duration of 5.3 ⫾ 4.9 years and a mean age of 47.8 ⫾ 14.1 years. Among them, 56.8% (54/95) were male. Patients with glomerular filtration rate (GFR) ⱖ 60 mL/min/1.73 m2 were selected for group 1 (n ⫽ 35), and those with GFR ⬍ 60 mL/min/1.73 m2 were selected for group 2 (n ⫽ 60). Demographic and clinical data were compared between groups. Serum and urine levels of p-cresol and indoxyl sulfate were also obtained. Results. Baseline serum p-cresol and indoxyl sulfate levels were significantly higher in advanced CKD stages (P ⫽ .001 and ⬍.0001, respectively). Patients at advanced CKD stages (group 2) had lower serum levels of hemoglobin and albumin (P ⬍ .0001), but higher levels of total cholesterol, triglyceride, and uric acid levels (P ⫽ .04, .04 and .001, respectively). Body mass index, C-reactive protein, and serum calcium and phosphate levels showed no significant differences between groups. The cut-off value for serum p-cresol between groups was 1.28 umol/L (P ⫽ .01), and that for the indoxyl sulfate level was 0.98 umol/L (P ⫽ .0001). Conclusion. The serum p-cresol and indoxyl sulfate levels were significantly higher in advanced CKD stages in transplant recipients. To evaluate the use of serum p-cresol and indoxyl sulfate levels as a predictive tool for survival, larger clinical studies are needed. VEN with improved immunosuppressive agents and early graft survival, graft function still deteriorates due to time-dependent immunologic and nonimmunologic causes in kidney transplant patients.1–3 The protein-bound uremic toxins (p-cresol and indoxyl sulfate) markedly accumulated in serum4 are associated with progression of renal failure in chronic kidney disease (CKD) patients.5,6 The ability of p-cresol and indoxyl sulfate to increase endothelial microparticle (EMP) release,7 which is associated with the increase of endothelial activation marker levels and impaired vascular function in uremic patients,8 suggested that specific uremic toxins may be involved in EMP increase and subsequent cardiovascular outcomes.9 –11 However, whether pcresol and indoxyl sulfate have a clinical impact such as this in transplant recipients is unknown. We conducted a cross-

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© 2012 Published by Elsevier Inc. 360 Park Avenue South, New York, NY 10010-1710 Transplantation Proceedings, 44, 621– 624 (2012)

sectional study to analyze the correlation between uremic toxins and renal function deterioration in kidney transplantation patients.

From the Division of Nephrology (S.-T.H., K.-H.S., C.-H.C., M.-J.W., T.-M.Y., Y.-W.C., C.-H.C.), Department of Internal Medicine, Taichung Veterans General Hospital; School of Medicine College of Medicine (T.-M.Y., C.-H.C.), China Medical University; School of Medicine, College of Medicine (K.-H.S., C.-H.C., M.-J.W., C.-H.C.), Chung Shan Medical University, Taichung, Taiwan. Address reprint requests to Cheng-Hsu Chen, MD, PhD, Division of Nephrology, Department of Internal Medicine, Taichung Veterans General Hospital, 160, Section 3, Taichung-Kang Rd, Taichung, 407, Taiwan. E-mail: [email protected] 0041-1345/–see front matter doi:10.1016/j.transproceed.2011.11.023 621

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HUANG, SHU, CHENG ET AL Table 1. Demographic Characteristics of the Study Population

Variable

Transplant Duration, y Age, y Male gender, n (%) Body mass index (kg/m2) Presence of CVD, n (%) CAD VHD CVA Diabetes mellitus, n (%) Hepatitis B, n (%) Hepatitis C, n (%) Smoking, n (%) CKD stage, n (%) 1 2 3 4 5

Group 1 (eGFR ⱖ 60 mL/min/1.73 m2) (N ⫽ 35)

Group 2 (eGFR ⬍ 60 mL/min/1.73 m2) (N ⫽ 60)

Total Patients (N ⫽ 95)

P Value

4.13 ⫾ 3.20 48.06 ⫾ 15.38 27 (77.1%) 24.30 ⫾ 4.12

6.06 ⫾ 5.50 47.60 ⫾ 13.45 27 (45.0%) 23.01 ⫾ 3.97

5.35 ⫾ 4.86 47.77 ⫾ 14.12 54 (56.8%) 23.43 ⫾ 4.04

NS NS .002 NS

2 (5.7%) 1 (2.9%) 0 (0.0%) 9 (25.7%) 6 (17.1%) 3 (8.6%) 5 (14.3%)

8 (12.9%) 4 (6.5%) 1 (1.6%) 15 (25.0%) 4 (6.7%) 11 (18.3%) 8 (13.3%)

10 (10.3%) 5 (5.2%) 1 (1.0%) 24 (25.3%) 10 (10.5%) 14 (14.7%) 13 (13.7%)

NS

2 (5.7%) 33 (94.3%) 0 (0.0%) 0 (0.0%) 0 (0.0%)

0 (0.0%) 2 (3.3%) 46 (76.%) 12 (20.0%) 1 (1.6%)

2 (2.1%) 35 (36.8%) 46 (48.4%) 12 (12.6%) 1 (1.0%)

⬍.0001

NS NS NS NS

Data are expressed as means ⫾ SD. Abbreviations: eGFR, estimated glomerular filtration rate; CVD, cardiovascular disease; CAD, coronary artery disease; VHD, valvular heart disease; CVA, cerebral vascular disease; CKD, chronic kidney disease; NS, not significant.

MATERIALS AND METHODS Patients The study population consisted of 95 kidney transplant recipients treated for at least 3 months between February 1987 and June 2011 in our center. The study was approved by the institutional review board and ethics committee (No.CE11155). Most patients were treated with triple-therapy immunosuppression in a maintenance dose that consisted of prednisolone in the case of 85 patients, either cyclosporine in the case of 19 patients or tacrolimus in the case of 75 patients, and either mycophenolate mofetil in the case of 37 patients or mycophenolate sodium in the case of 29 patients. Another 10 patients were also treated with sirolimus. Patients with a glomerular filtration rate (GFR) ⱖ 60 mL/min/1.73 m2 were

selected as group 1 (n ⫽ 35), and those with GFR ⬍ 60 mL/min/ 1.73 m2 were selected as group 2 (n ⫽ 60). Allograft function was differentiated according to the proposed National Kidney Foundation Kidney Disease Outcome Quality Initiative (KDOQI) clinical practice guidelines for CKD because all patients with a kidney transplant would be considered either to have CKD or to be at increased risk for CKD. Demographic, clinical, and biochemical data were compared between groups. Serum and urine levels of total p-cresol and indoxyl sulfate were also obtained.

STATISTICAL ANALYSIS Statistical analysis was performed with SPSS for Windows, version 16.0. Data are expressed as percent and mean ⫾ standard devia-

Table 2. Biochemical Characteristics of the Study Population

Variable

Group 1 (eGFR ⱖ 60 mL/min/1.73 m2) (N ⫽ 35)

Group 2 (eGFR ⬍ 60 mL/min/1.73 m2) (N ⫽ 60)

Total Patients (N ⫽ 95)

P Value

Urea, mg/dL Creatinine, mg/dL Hemoglobin, g/dL Albumin, g/dL CRP, mg/dL Calcium, mmol/dL Phosphate, mmol/dL Total cholesterol, mmol/dL Triglycerides, mmol/dL Uric acid, mg/dL Serum p-cresylsulfate, umol/L Serum indoxyl-sulfate, umol/L Urine p-cresylsulfate, umol/L Urine indoxyl-sulfate, umol/L

15.9 ⫾ 4.96 1.1 ⫾ 0.16 13.6 ⫾ 1.46 4.5 ⫾ 0.27 0.6 ⫾ 0.91 9.3 ⫾ 0.67 3.3 ⫾ 0.78 169.4 ⫾ 32.15 120.2 ⫾ 52.27 6.5 ⫾ 1.53 2.3 ⫾ 3.07 0.6 ⫾ 0.98 38.6 ⫾ 81.32 48.0 ⫾ 58.67

27.9 ⫾ 14.84 1.9 ⫾ 1.33 11.8 ⫾ 2.24 4.1 ⫾ 0.40 0.8 ⫾ 0.88 9.2 ⫾ 1.18 3.2 ⫾ 0.75 184.0 ⫾ 38.19 148.7 ⫾ 62.95 7.7 ⫾ 1.69 5.2 ⫾ 6.66 2.6 ⫾ 3.38 36.3 ⫾ 55.56 48.7 ⫾ 48.81

23.5 ⫾ 13.46 1.6 ⫾ 1.13 12.4 ⫾ 2.17 4.2 ⫾ 0.40 0.7 ⫾ 0.88 9.2 ⫾ 1.02 3.2 ⫾ 0.75 178.6 ⫾ 36.60 138.2 ⫾ 60.55 7.3 ⫾ 1.73 4.1 ⫾ 5.76 1.9 ⫾ 2.90 37.2 ⫾ 65.91 48.4 ⫾ 52.39

⬍.0001 ⬍.0001 ⬍.0001 ⬍.0001 NS NS NS .04 .04 .001 .02 ⬍.0001 NS NS

Data are expressed as means ⫾ SD. Abbreviations: eGFR, estimated glomerular filtration rate; CRP, C-reactive protein; NS, not significant.

P CRESOL AND INDOXYL LEVELS WITH CKD

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tion. Demographic and outcome differences were compared by Pearson’s chi-square test, Fisher exact test, Yate’s correction for continuity, the Mann-Whitney U test, and independent sample t test as appropriate. Linear regression analysis was used to assess the relationship between serum p-cresylsulphate levels and renal function. Serial biochemical changes were analyzed with the generalized estimating equation (GEE) model. A P value ⬍.05 was considered statistically significant.

RESULTS

The mean follow-up duration in group 1 was comparable to that in group 2 (4.1 ⫾ 3.2 years versus 6.0 ⫾ 5.5 years, P ⫽ .22). Age, sex, body mass index, prevalence of cardiovascular comorbidity, diabetes mellitus, hepatitis B or C infection, and smoking history were also comparable between groups. Most patients in group 1 were in CKD stage 2 (33; 94.3%), and most patients in group 2 were in CKD stage 3 (46; 76.7%; in Table 1). With regard to immunosuppressive regimens, the average prednisolone dose used in group 1

Fig 2. Comparision of eGFR levels at different serum p-cresol sulfate levels. * P ⬍ .05 between two groups. ** P ⬍ .05 for trend analysis by GEE (generalized estimating equation) model.

Fig 1. The correlation of serum p-cresol sulfate and indoxyl sulfate (umol/L) and stage of chronic kidney disease (CKD) in renal transplant recipients. P ⫽ .001 and P ⬍ .0001, respectively.

was lower than that used in group 2 (4.8 ⫾ 1.8 mg/d versus 6.1 ⫾ 4.1 mg/d, P ⫽ .01). The average dose and trough concentration of tacrolimus, cyclosporine, and sirolimus were not significantly different between groups. The serum p-cresol and indoxyl sulfate concentrations were lower in group 1 than in group 2 (2.3 ⫾ 3.1 umol/L versus 5.2 ⫾ 6.7 umol/L, P ⫽ .02; 0.6 ⫾ 1.0 umol/L versus 5.2 ⫾ 6.7 umol/L, P ⫽ .02, respectively; Table 2). Serum hemoglobin and albumin levels were significantly higher in group 1 than in group 2 (13.6 ⫾ 1.5 versus 11.8 ⫾ 2.2 g/dL, P ⬍ .0001; 4.5 ⫾ 0.3 versus 4.1 ⫾ 0.4 g/dL, P ⬍ .0001, respectively). The serum cholesterol, triglyceride, and uric acid levels were significantly lower in group 1 than in group 2 (P ⫽ .04, P ⫽ .04 and P ⬍ .0006, respectively). We also found that the serum level of p-cresol and indoxyl sulfate was higher at advanced CKD stages (Fig 1). There was no difference associated with eGFR (data not shown).

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Table 3. Correlations Between Serum p-Cresol and Indoxyl Sulphate and Selected Clinical and Biochemical Characteristics p-Cresol Sulfate

Albumin, g/dL Serum indoxyl-sulfate, umol/L Urine p-cresol sulfate, umol/L Creatinine, mg/dL Prednisolone dose (mg) Serum p-cresol sulfate, umol/L Urine indoxyl-sulfate, umol/L

␤

P

⫺3.27 1.09

.0009 ⬍.0001

0.04

⬍.0001

ration of renal function at different levels of serum p-cresol and indoxyl sulfate with time. In conclusion, the function progression and malnutrition in kidney transplant patients.

Indoxyl Sulfate

␤

P

2.12 ⫺0.26 0.17

⬍.0001 .0007 ⬍.0001

0.01

.0329

The cut-off values of the serum p-cresol and indoxyl sulfate levels between groups were 1.28 umol/L and 0.98 umol/L, respectively (Fig 2, P ⫽ .001 and .0001 by ROC curve). Linear regression analysis revealed that there was an inverse correlation between the serum p-cresol level and serum albumin level, and a positive correlation between the serum p-cresol level and serum indoxyl sulfate and urine p-cresol levels. The serum indoxyl sulfate level was positively correlated with the serum creatinine level and inversely correlated with the daily prednisolone dose (Table 3). DISCUSSION

Our study presented the distribution of serum p-cresol and indoxyl sulfate levels at different stages of CKD in transplant recipients. Renal function appeared to be an important determining factor of the indoxyl sulfate level in these patients, which shows the ability of p-cresol and indoxyl sulfate to induce oxidation damage in endothelial cells12 and worsen renal function. We also found that the serum albumin level, a nutrition marker, was inversely associated with the serum p-cresol level. Further studies are needed to confirm whether p-cresol is associated with cachexia, as we would see in the elevation of cytokines such as leptin in uremic patients,13 or was an innocent bystander only. On the other hand, cardiovascular disease (CVD) accounts for graft failure and for up to 25% of patient death after kidney transplantation. In a subanalysis of the Folic Acid for Vascular Outcome Reduction in Transplantation (FAVORIT) study,14 the researchers found that cardiovascular risk factors, especially uncontrolled hypertension, were undertreated in kidney transplantation patients. Apart from strategies to reduce cardiovascular risk, such as early corticosteroid withdrawal15,16 and improving compliance, we focused on the role of uremic toxins as a novel CVD risk factor17–22 and its contribution to the progression of CKD.5,6 Although we did not evaluate the relationship between the accumulation of uremic toxins and subsequent cardiovascular outcome because of the small study population and short follow-up duration, we showed the deterio-

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