American Journal of Kidney Diseases
Volume 54, Issue 6 , Pages 1062-1071, December 2009

Association of Soluble Endotoxin Receptor CD14 and Mortality Among Patients Undergoing Hemodialysis

  • Dominic S.C. Raj, MD

      Affiliations

    • George Washington University School of Medicine, North Washington, DC
    • ,
  • Vallabh O. Shah, PhD

      Affiliations

    • Department of Biochemistry, University of New Mexico Health Sciences Center, Albuquerque, NM
    • ,
  • Mehdi Rambod, MD

      Affiliations

    • Harold Simmons Center for Chronic Disease Research and Epidemiology at Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA
    • ,
  • Csaba P. Kovesdy, MD

      Affiliations

    • Department of Medicine, Veteran Administrations Medical Center, Salem, VA
    • ,
  • Kamyar Kalantar-Zadeh, MD, MPH, PhD

      Affiliations

    • Harold Simmons Center for Chronic Disease Research and Epidemiology at Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA
    • Corresponding Author InformationAddress correspondence to Kamyar Kalantar-Zadeh, MD, MPH, PhD, Harold Simmons Center for Chronic Disease Research and Epidemiology, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, and UCLA David Geffen School of Medicine and UCLA School of Public Health, 1124 West Carson St, C1-Annex, Torrance, CA 90502

Received 4 February 2009; accepted 22 June 2009. published online 21 August 2009.

Article Outline

Background

CD14 is a key molecule in innate immunity that mediates cell activation and signaling in response to endotoxin and other bacterial wall-derived components. CD14 protein exists in soluble (sCD14) and membrane-bound forms. The correlates of sCD14 in persons undergoing long-term hemodialysis (HD) therapy are not known. We hypothesized that increased sCD14 levels in HD patients are associated with proinflammatory cytokine activation and increased mortality.

Study Design

Cohort study.

Setting & Participants

310 long-term HD patients who participated in the Nutritional and Inflammatory Evaluation in Dialysis (NIED) Study, a cohort derived from a pool of more than 3,000 HD outpatients during 5 years in 8 DaVita maintenance dialysis facilities in the South Bay Los Angeles, CA, area.

Predictors

sCD14 levels in serum.

Outcomes

33-month mortality.

Results

Mean sCD14 level was 7.24 ± 2.45 μg/mL. Tumor necrosis factor α level was the strongest correlate of sCD14 level (r = +0.24; P < 0.001), followed by interleukin 6 level (r = +0.18; P = 0.002), serum ferritin level (r = +0.21; P < 0.001), total iron-binding capacity (r = −0.19; P < 0.001), body mass index (r = −0.15; P = 0.008), vintage (r = +0.14; P = 0.01), low-density lipoprotein cholesterol level (r = +0.13; P = 0.03), and body fat (r = −0.11; P = 0.06). During the 33-month follow-up, 71 (23%) patients died. Multivariable Cox proportional analysis adjusted for case-mix and other nutritional and inflammatory confounders, including serum tumor necrosis factor α, C-reactive protein, and interleukin 6 levels, showed that compared with the lowest sCD14 tertile, sCD14 levels in the third tertile (>7.8 μg/mL) were associated with greater death risk (hazard ratio, 1.94; 95% confidence interval, 1.01 to 3.75; P = 0.04).

Limitations

Survivor bias in combined incident/prevalent studies.

Conclusions

Increased sCD14 level is related positively to markers of inflammation and negatively to nutritional status and is an independent predictor of mortality in long-term HD patients. Additional studies are needed to examine the usefulness of sCD14 level in risk stratification and the clinical decision-making process in HD patients.

Index Words: Hemodialysis, mortality, inflammation, endotoxin, soluble CD14, mortality, nutritional status

 

Editorial, p. 990

Currently, there are approximately 400,000 patients with end-stage renal disease (ESRD) on dialysis therapy in the United States. Despite the magnitude of the resources allotted to the care of patients with ESRD, they continue to experience significant mortality and morbidity. Although the cause of increased mortality in patients with ESRD is a topic of intense debate and an intriguing research domain, there is consensus among investigators that inflammation is a key factor. However, the cause of the unbalanced activation of proinflammatory cytokines with a decrease in renal function is speculative. One potentially important source of inflammation in patients with ESRD is subclinical endotoxemia.1, 2 The presence of very low levels of endotoxin or endotoxin fragments in dialysate is capable of inducing the production of cytokines.3, 4 In vitro studies show that a lipopolysaccaride (LPS) concentration as low as 0.01 ng/mL induces upregulation of CD14 expression.5 CD14 is a key molecule in innate immunity that is expressed constitutively in considerable amounts on the surface (membrane-bound CD14 [mCD14]) of mature monocytes, macrophages, and neutrophils.6 Binding of LPS to the complex of mCD14 and Toll-like receptor 4 at the surface of innate immune cells triggers the secretion of proinflammatory cytokines. A soluble form of CD14 (sCD14) is present in serum and is derived from both secretion of CD14 and enzymatically cleaved glycosyl-phosphatidylinositol–anchored tissue CD14.7, 8

Protein-energy wasting is present in approximately 40% of patients treated with maintenance dialysis and consistently has been found to be a strong predictor of the high morbidity and mortality observed in this population.9 Inflammation coexists with protein-energy wasting and cardiovascular disease in patients with ESRD.10 Increased endotoxin and CD14 expression have been linked to inflammation and increased cardiovascular disease in the general population.11 However, the clinical significance of sCD14 levels in patients with ESRD in North America has not been explored. To test the hypothesis that increased sCD14 levels are associated with increased mortality in patients with ESRD, we measured plasma sCD14 in a well-defined cohort of 310 patients undergoing thrice-weekly in-center hemodialysis (HD). We hypothesized that sCD14 level is an independent predictor of mortality and is associated positively with markers of inflammation and negatively with nutritional status in US patients with ESRD.

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Methods 

Patient Population 

We studied long-term HD patients who participated in the Nutritional and Inflammatory Evaluation in Dialysis (NIED) Study.12 The original patient cohort was derived from a pool of more than 3,000 HD outpatients during 5 years in 8 DaVita maintenance dialysis facilities in the South Bay Los Angeles, CA, area (see the NIED Study website at www.NIEDStudy.org for more details, as well as previous publications13, 14, 15). Inclusion criteria were outpatients who had been undergoing HD treatment for at least 8 weeks, were 18 years or older, and had signed the institutional review board–approved consent form. Patients with acute infections or an anticipated life expectancy less than 6 months (eg, because of metastatic malignancy or advanced HIV/AIDS disease) were excluded. A total of 893 long-term HD patients participated in the NIED Study during the course of 5 years (October 2001 to December 2006). From April 1 through September 30, 2004, a total of 310 long-term HD patients who had signed the informed consent form underwent all tests and evaluations for this study. The medical chart of each HD patient was reviewed thoroughly by a collaborating physician, and data pertaining to the underlying kidney disease, cardiovascular history, and other comorbid conditions were extracted. A modified version of the Charlson Comorbidity Index, ie, without the age and kidney disease components, was used to assess the severity of comorbidities.16, 17 The 310 HD patients were followed up for up to 33 months, ie, until December 31, 2006.

Anthropometric and Dietary Measures 

Body weight assessment and anthropometric measurements were performed while patients underwent an HD treatment or within 5 to 20 minutes after termination of the treatment. Biceps skinfold and triceps skinfold thicknesses were measured by means of a conventional skinfold caliper using standard techniques, as previously described.18, 19

Near-Infrared Interactance 

To estimate percentages of body fat and fat-free body mass, near-infrared (NIR) interactance was measured at the same time as anthropometric measurements.20 A commercial NIR interactance sensor with a coefficient of variation of 0.5% for total body fat measurement (portable Futrex 6100; Futrex, Inc, Rockville, VA; www.futrex.com) was used. NIR measurements were performed by placing a Futrex sensor on the upper aspect of the arm without a vascular access for several seconds and entering the required data (date of birth, sex, weight, and height) for each patient. NIR measurements of body fat appear to correlate significantly with other nutritional measures in HD patients.13

sCD14 Measurement 

sCD14 was measured by using a commercially available enzyme-linked immunosorbent assay (ELISA) kit (sCD14 Quantikine ELISA Kit; R&D Systems, Minneapolis, MN). Interassay and intra-assay coefficients of variation are less than 7.5% and less than 6.5%, respectively. All samples were measured in triplicate, and the mean value was reported in micrograms per milliliter.

Other Laboratory Tests 

Predialysis blood samples and postdialysis serum urea nitrogen samples were obtained on a midweek day that coincided chronologically with the drawing of quarterly blood tests in DaVita facilities. Single-pool Kt/V was used to represent weekly dialysis dose. All routine laboratory measurements were performed by DaVita Laboratories (Deland, FL) by using automated methods.

Serum high-sensitivity C-reactive protein (CRP) was measured by using a turbidometric immunoassay (WPCI, Osaka, Japan; normal range, <3.0 mg/L).21, 22 Interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α) were measured by using immunoassay kits based on a solid-phase sandwich ELISA using recombinant human IL-6 and TNF-α (R&D Systems; normal range: IL-6, <9.9 pg/mL; TNF-α, <4.7 pg/mL).23, 24 CRP, TNF-α, and IL-6 were measured in the General Clinical Research Center Laboratories of Harbor-UCLA. Serum transthyretin (prealbumin) was measured by using immunoprecipitation analysis. Plasma total homocysteine concentrations were determined by means of high-performance liquid chromatography in the Harbor-UCLA Clinical Laboratories.

Statistical Methods 

Pearson correlation coefficient (r) was used for analyses of linear associations. Multivariate regression analyses and analyses of covariance were performed to obtain adjusted P values controlled for case-mix and other covariates. Restricted cubic splines graphs were used as exploratory data analysis strategies to illustrate systematic relations of sCD14 level with mortality. This method also served to examine nonlinear associations as continuous mortality predictors as an alternative to inappropriate linearity assumptions.25 Thereafter, to calculate relative risks of death, hazard ratios (HRs) were obtained by using Cox proportional hazard models after controlling for the relevant covariates. Plots of log (−log [survival rate]) against log (survival time) were performed to establish the validity of the proportionality assumption. Kaplan-Meier analyses were used to assess differences in surviving proportions between tertiles of sCD14 levels. A stepwise linear regression model including all relevant variables was used to examine the best predictors of sCD14 level as a dependent variable.

Case-mix covariates included sex, age, race, and ethnicity (Hispanic, African American, Asian, and other), diabetes mellitus, and dialysis vintage. Laboratory measures of malnutrition-inflammation-cachexia syndrome (MICS) included albumin, creatinine, hemoglobin, total iron-binding capacity, normalized protein catabolic rate, lymphocyte percentage, and body mass index (BMI); the fully adjusted Cox models included serum CRP, TNF-α, and IL-6 levels in addition to case-mix and MICS variables. Fiducial limits are given as mean ± SD or median and interquartile range; risk ratios include 95% confidence intervals (CIs). P < 0.05 or a 95% CI that did not span 1.0 was considered to be statistically significant. Descriptive and multivariate statistics were carried out by using Stata statistical software, version 10.0 (Stata Corp, College Station, TX).

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Results 

The 310 participants in the study were 55.1 ± 14.7 years old and included 48% women, 52% Hispanics, 30% African Americans, and 57% patients with diabetes. Mean dialysis vintage was 50 ± 35 months (median, 45 months; quartile [Q] 1 to Q3, range, 25 to 68). Mean sCD14 level was 7.24 ± 2.45 μg/ml. Table 1 lists relevant demographic, clinical, and laboratory measures across tertiles of sCD14. Age, dialysis vintage, and levels of serum alkaline phosphatase, ferritin, homocysteine, and the 3 proinflammatory markers, CRP, IL-6, and TNF-α, were greater in patients in the third (highest) sCD14 tertile. However, there was no difference across tertiles in terms of sex, race/ethnicity, and diabetes mellitus. Anthropometric measures, including BMI, triceps and biceps skin folds, midarm circumference, and NIR-measured body fat, were lower in patients in the third tertile of sCD14. The same decreasing trend was observed for albumin, prealbumin, and total iron-binding capacity values. There was no trend for white blood cell counts, lymphocyte percentages, or iron saturation ratios across tertiles of sCD14.

Table 1. Baseline Demographic, Clinical, and Laboratory Values in Total and According to Tertiles of Soluble Endotoxin Receptor CD14 in 310 Maintenance Hemodialysis Patients
VariableTertiles of Soluble Endotoxin Receptor CD14P for Trend
1; <6 μg/mL (n = 103)2; 6-7.84 μg/mL (n = 104)3; >7.84 μg/mL (n = 103)
Demographic
Age (y)52.7±14.956.2±14.256.4±14.90.08
Women (%)5247460.4
Race (% African American)3220370.5
Ethnicity (% Hispanic)4863460.8
Primary insurance (% Medicare)4955520.7
Diabetes mellitus (%)5863500.2
Modified Charlson comorbidity score1.2±1.21.7±1.52.2±1.60.8
Crude mortality rate⁎ (%)1422330.001
Body composition
Body mass index (kg/m2)27.1±7.326.3±5.924.9±5.10.01
Triceps skinfold (mm)19.6±11.417.2±9.913.9±7.8<0.001
Biceps skinfold (mm)10.3±8.19.4±7.37.9±6.00.02
Midarm circumference (cm)31.8±6.431.0±5.729.6±5.30.01
Near-infrared measured body fat (%)28.4±10.928.1±10.625.7±10.60.08
Hemodialysis treatment measures
Dialysis vintage (mo)43.8±34.351.9±35.354.4±35.30.006
Dialysis dose (single-pool Kt/V)1.67±0.291.71±0.301.71±0.250.3
nPCR (g/kg/d)1.10±0.221.10±0.281.07±0.240.3
Erythropoietin dose (1,000 U/wk)15.0±16.212.7±10.315.1±15.50.6
Biochemical measurements
Serum albumin (g/dL)4.0±0.34.0±0.43.9±0.40.05
Prealbumin (transthyretin) (mg/dL)30.3±8.429.4±8.928.3±8.30.1
Creatinine (mg/dL)10.3±2.79.6±2.79.9±2.80.3
Total iron-binding capacity (mg/dL)213±35208±37198±330.003
Calcium (mg/dL)9.7±0.79.6±0.69.6±0.60.2
Phosphorus (mg/dL)5.7±1.25.4±1.35.6±1.50.4
Alkaline phosphatase (U/L)115±56126±66140±1020.02
Iron saturation ratio33.3±10.435.0±12.135.0±12.50.3
Ferritin (ng/mL)500±332656±422728±353<0.001
Total homocysteine (μmol/L)24.2±7.125.5±8.127.2±8.80.008
Low-density lipoprotein cholesterol (mg/dL)75.6±30.278.9±31.183.3±35.40.1
High-density lipoprotein cholesterol (mg/dL)39.1±13.135.5±12.835.2±12.40.04
Total cholesterol (mg/dL)142±40148±41147±470.4
Triglycerides (mg/dL)141±108176±165143±920.9
C-Reactive protein (mg/L)4.1±5.14.9±5.45.8±6.20.01
Interleukin 6 (pg/mL)8.8±12.59.7±10.313.0±16.90.006
Tumor necrosis factor α (pg/mL)2.2±0.82.5±0.82.8±1.2<0.001
Blood hemoglobin (g/dL)12.2±0.812.1±0.812.1±0.90.5
White blood cells (×103/μL)7.0±2.26.9±1.76.7±2.00.3
Lymphocytes (%total white blood cells)23.8±8.123.4±6.523.5±8.10.7

Note: Values expressed as mean±SD or percentage. P values for dialysis dose (vintage), ferritin level, vitamin D dose, C-reactive protein level, interleukin 6 level, and tumor necrosis factor α level are based on the logarithmic values of these measures. Conversion factors for units: albumin in g/dL to g/L, ×10; creatinine in mg/dL to μmol/L, ×88.4; calcium in mg/dL to mmol/L, ×0.2495; phosphorus in mg/dL to mmol/L, ×0.3229; homocysteine in μmol/L to mg/L, ×0.1352; total, low-density lipoprotein, and high-density lipoprotein cholesterol in mg/dL to mmol/L, ×0.02586; triglycerides in mg/dL to mmol/L, ×0.01129; hemoglobin in g/dL to g/L, ×10. Ferritin in ng/mL and μg/L and white blood cell count in 103/μL and 109/L require no conversion.

Abbreviations: Kt/V, dialysis dose; nPCR, normalized protein catabolic rate.

⁎Mortality pertains to a maximum of 33 months.

Correlates of sCD14 

Table 2 lists correlations between sCD14 levels and some relevant nutritional, inflammatory, and other biochemical variables. Of all variables, patient age, dialysis treatment age (vintage), and levels of serum ferritin, TNF-α, IL-6, and low-density lipoprotein cholesterol (LDL-C) correlated positively with sCD14 levels, and these correlations were robust to multivariate adjustment. TNF-α level had the strongest correlation with sCD14 level (Fig 1). Other variables, including BMI and serum total iron-binding capacity, correlated negatively with sCD14 levels. Although sCD14 level initially appeared weakly correlated with serum creatinine level (r = −0.09; P = 0.1) and logarithm (log) of parathyroid hormone (r = −0.07; P = 0.2), multivariate-adjusted associations were stronger after controlling for age, sex, diabetes mellitus, log vintage, log IL-6, and log TNF-α (creatinine, r = −0.13; P = 0.03; log parathyroid hormone, r = −0.13; P = 0.02). Figure 2 also shows significant decreasing trends of sCD14 levels across categories of body fat (upper panel) and BMI (lower panel).

Table 2. Bivariate (unadjusted) and Partial (adjusted) Correlation Coefficients Between Soluble Endotoxin Receptor CD14 and Relevant Variables in 310 Maintenance Hemodialysis Patients
VariableBivariate CorrelationPAdjusted Correlation⁎P
Age0.070.20.120.04
Dialysis vintage (log scale)0.140.010.110.07
Body mass index−0.150.008−0.150.009
Normalized protein catabolic rate−0.060.3−0.010.9
Near-infrared body fat percentage−0.110.06−0.140.02
Serum calcium−0.040.5−0.030.6
Phosphorus−0.050.4−0.040.5
Intact parathyroid hormone (log scale)−0.070.2−0.130.02
Alkaline phosphatase0.050.4−0.010.9
Albumin−0.130.02−0.080.2
Transthyretin−0.090.1−0.040.5
Total iron-binding capacity−0.19<0.001−0.120.04
Ferritin0.21<0.0010.190.001
Creatinine−0.090.1−0.130.03
Interleukin 6 (log scale)0.180.0020.140.02
Tumor necrosis factor α (log scale)0.24<0.0010.22<0.001
C-Reactive protein (log scale)0.140.020.060.3
Low-density lipoprotein cholesterol0.130.030.130.03
High-density lipoprotein cholesterol−0.060.3−0.020.7
Total cholesterol0.100.090.110.06
Triglycerides0.010.90.020.8
Blood hemoglobin−0.050.4−0.020.7
White blood cells−0.040.5−0.050.4
Percentage lymphocytes−0.050.4−0.060.3

⁎In the adjusted analysis, age, sex, diabetes, log interleukin 6, log tumor necrosis factor α, and log vintage were included as covariates.

  • View full-size image.
  • Figure 1. 

    Scatter plots, regression line, and 95% confidence intervals reflecting correlations between serum levels of soluble endotoxin receptor CD14 (sCD14) and values for serum ferritin, total iron-binding capacity, log for interleukin 6, and log for tumor necrosis factor α.

Serum sCD14 and Survival 

During the 33-month follow-up, 71 (23%) patients died, 33 (11%) underwent transplantation, and 26 (8%) left the cohort. Figure 3 shows cubic splines illustrating associations between baseline sCD14 level and mortality in the 33-month cohort of 310 HD patients. A consistent trend toward increased death risk was observed in patients with greater sCD14 levels, even after multivariate adjustment for other makers of nutrition and inflammation, including CRP, IL-6, and TNF-α levels (Fig 3D). As shown in Fig 4, Kaplan-Meier survival plots showed incrementally worsening survival across increasing sCD14 tertiles. The calculated death HRs listed in Table 3 indicated that maintenance HD patients in the third tertile of sCD14 levels had a 2-fold greater death risk versus those in the first tertile (HR, 2.59; 95% CI, 1.39 to 4.83; P = 0.003), and this trend was robust to multivariate adjustment for other measures of MICS, including levels of several inflammatory markers and cytokines (HR, 1.94; 95% CI, 1.01 to 3.75; P = 0.046).

  • View full-size image.
  • Figure 3. 

    Mortality predictability of soluble endotoxin receptor CD14 in 310 maintenance hemodialysis patients (April 2004 to January 2007). Case-mix variables: age, sex, race/ethnicity, diabetes mellitus, and log vintage. Malnutrition-inflammation-cachexia syndrome (MICS) variables: values for albumin, creatinine, hemoglobin, normalized protein catabolic rate (nPCR), lymphocyte percentage, and body mass index. The fully adjusted model included serum CRP, tumor necrosis factor α, and interleukin 6 levels in addition to case-mix and MICS variables.

  • View full-size image.
  • Figure 4. 

    Kaplan-Meier proportion surviving after 2.8 years of observation according to tertiles of soluble endotoxin receptor CD14 in 310 hemodialysis patients (April 2004 to January 2007).

Table 3. HRs of 33-Month Mortality According to Tertiles of Soluble Endotoxin Receptor CD14 in 310 Maintenance Hemodialysis Patients
UnadjustedCase-Mix⁎ AdjustedCase-Mix + MICS† AdjustedCase-Mix + MICS + Inflammation Adjusted (full model)‡
CD14 TertilesDeaths (no.)HR (95% CI)PHR (95% CI)PHR (95% CI)PHR (95% CI)P
1: <6 μg/mL (n = 103)141.00 (reference)1.00 (reference)1.00 (reference)1.00 (reference)
2: 6-7.84 μg/mL (n = 104)231.52(0.78-2.98)0.21.46(0.74-2.89)0.21.37(0.68-2.74)0.31.26(0.62-2.53)0.5
3: >7.8 μg/mL (n = 103)342.59(1.39-4.83)0.0032.49(1.33-4.68)0.0042.09(1.09-4.00)0.021.94(1.01-3.75)0.04

Abbreviations: CI, confidence interval; HR, hazard ratio; MICS, malnutrition-inflammation-cachexia syndrome.

⁎Case-mix variables include age, sex, race/ethnicity, diabetes, and log vintage.

†MICS variables include values for albumin, creatinine, hemoglobin, total iron-binding capacity, normalized protein catabolic rate, lymphocyte percentage, and body mass index.

‡Full model consists of case-mix and MICS variables and logarithm of 3 inflammatory markers: C-reactive protein, interleukin 6, and tumor necrosis factor α.

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Discussion 

In this cohort of 310 long-term HD outpatients in Southern California, we found that greater circulating sCD14 level is associated with greater 33-month death risk. The increasing trend of mortality associated with greater sCD14 levels was robust to controlling for case-mix and other nutritional and inflammatory measures, including serum IL-6 and TNF-α levels. Maintenance HD patients in the third tertile of sCD14 levels had an almost-2 fold increased death risk (HR, 1.94) after adjustment for other confounders. Lower BMI and white blood cell count and higher LDL-C, ferritin, IL-6, and TNF-α levels were the strongest correlates of sCD14 variability. These findings imply that sCD14 level may be a useful and robust marker of inflammatory and nutritional status, with a strong association with survival.

Endotoxin, the hydrophobic anchor of LPS, is a glucosamine-based phospholipid that makes up the outer monolayer of the outer membranes of most Gram-negative bacteria.26 On entry into the bloodstream, LPS is complexed to LPS-binding protein, and the resulting complex then recognizes the cell-surface CD14 antigen on monocytes/macrophages, leading to enhanced cytokine production.27 Mean sCD14 level was 7.24 ± 2.45 μg/mL in our study population. Nockher and Scherberich5 reported that serum sCD14 levels are approximately 2.5-fold greater in patients with ESRD compared with healthy controls. Using in vitro studies, they showed that enhanced expression of CD14 by monocytes after HD and increased sCD14 serum levels are caused by long-term exposure to trace amounts of endotoxin. Thus, the increased sCD14 serum concentrations in HD patients possibly are caused by repeated stimulation of CD14 expression by subclinical endotoxemia with subsequent release of sCD14 during each dialysis session.5 The physiological importance of increased sCD14 serum levels in HD patients is not yet clear, but is complex and cell specific. sCD14 is believed to have a key role in the neutralization of LPS under physiological conditions and attenuate the inflammatory response.28 During endotoxemia, sCD14 partially inhibits the immune response of macrophages that constitutively express mCD14,29 but promotes the response of cells that do not express mCD14.30 Endotoxemia and increased plasma sCD14 levels are associated with inflammation, insulin resistance,31, 32 muscle wasting,33 atherosclerosis, and cardiovascular disease.11, 34 These results indicate that some clinical consequences of endotoxemia are mediated by increased sCD14 levels.

Szeto et al1 reported that subclinical endotoxemia is common in peritoneal dialysis patients, and the degree of circulating endotoxemia is associated with systemic inflammation and atherosclerosis. Heine et al35 observed that the number of CD14++CD16+ monocytes was independently associated with cardiovascular events and death in dialysis patients. We observed that sCD14 levels were related positively to markers of inflammation and negatively to anthropometric measures. A stepwise linear model showed that BMI, LDL-C, ferritin, white blood cell count, IL-6, and TNF-α levels could account for up to 20% of the variance in sCD14 levels in the study population. In healthy men and patients with type 2 diabetes, serum sCD14 concentration is not related to BMI.31 However, in our study population, we noted that BMI and body fat determined by means of NIR were negatively and significantly related to sCD14 levels. In contrast to reports of the general population,36 greater BMI is associated with better outcomes in patients with ESRD.37 The superiority of muscle mass over fat mass in conferring survival advantage is disputed13, 33; however, depletion of both could have adverse consequences.38, 39, 40 Increased sCD14 level was associated with increased death risk, which persisted even after multivariate adjustment for other markers of nutrition and inflammation, including CRP, IL-6, and TNF-α levels.

It is important to note that one of the coauthors of this report recently examined correlates of sCD14 in a Swedish cohort of HD patients and reported similar findings.41 Median sCD14 level in the Swedish cohort was 3.2 μg/mL (Q1 to Q3, 2.7 to 3.9), whereas in our cohort, it is 6.8 μg/mL (Q1 to Q3, 5.7 to 8.6). This difference may be caused by demographic distinctions in that HD patients in the present study are representative of the US dialysis population and consist of persons of diverse ethnicity, a greater proportion of patients with diabetes, and a greater percentage of tunneled catheters or arteriovenous grafts as vascular access, whereas the European cohort study41 consists of white Swedish individuals and fewer patients with diabetes, and most participants have arteriovenous fistulas and better nutritional status. Furthermore, differences in dialysis membrane flux or reuse practice may have had a role, especially because during the NIED Study era, dialysis membranes were reused a median of 12 times (Q1 to Q3, 8 to 17).

Our study should be qualified for a number of limitations, including selection bias during enrollment leading to younger maintenance HD patients. Furthermore, we do not have measurements of circulating endotoxin. However, because mortality in the original NIED Study cohort was less than in the base population,12 it might be argued that selection bias with such a direction generally would lead to bias toward the null, so that without this bias, our positive results might have been even stronger. A strength of our cohort is that participants were selected randomly without prior knowledge of inflammation status. Moreover, our study includes a moderate sample size; comprehensive clinical and laboratory evaluations, including body composition measures; detailed evaluation of comorbid states by study physicians; and measurement of proinflammatory cytokines. Finally, the same blood specimens used to measure serum markers of nutrition and inflammation were used for sCD14 measurements.

To summarize, this study shows that levels of the endotoxin receptor sCD14 correlated with several surrogates of body composition and inflammation. We found that a 1-μg/mL increase in serum sCD14 level is accompanied by a virtually 2-fold increased death risk in long-term HD patients. In addition, TNF-α level was the strongest correlate of sCD14 level, followed by IL-6, serum ferritin, total iron-binding capacity, BMI, vintage, and LDL-C values. Understanding the role of sCD14 and its contribution to morbidity and mortality in the long-term HD population may lead to more useful strategies for risk stratification of long-term HD patients based on inflammatory status and death risk. Hence, future investigations are needed to elucidate the role of sCD14 in the inflammatory cascade of long-term HD patients.

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Acknowledgements 

The authors thank Ms Stephanie Griffith and Dr Victor Goh at Harbor-UCLA GCRC Core Laboratories for the management of blood samples and measurement of inflammatory markers; the hard-working collaborating dietitians in 10 DaVita dialysis facilities in Los Angeles South Bay area; and DaVita teammates in these facilities.

Some data were presented during the Spring Clinical Meeting of the National Kidney Foundation in March 25-29, 2009 in Nashville, TN.

Support: This study was supported by National Institutes of Health (NIH), National Institute of Diabetes and Digestive and Kidney Disease Grants R21-DK61162 and K23-DK061162 (for Dr Kalantar-Zadeh). Additional sources of funding include research grants from Watson Pharmaceuticals, DaVita Clinical Research, a philanthropist grant by Mr Harold Simmons (for Dr Kalantar-Zadeh), and General Clinical Research Center Grant No. M01-RR00425 from the National Centers for Research Resources, NIH. sCD14 analysis was supported by NIH Grant R01DK073665 and a Norman Coplon Research grant (to Dr Raj).

Financial Disclosure: None.

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References 

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 Originally published online as doi:10.1053/j.ajkd.2009.06.028 on August 21, 2009.

PII: S0272-6386(09)00967-6

doi:10.1053/j.ajkd.2009.06.028

Refers to article:

  • Soluble CD14 and Endotoxin Levels in Hemodialysis Patients: A Tale of 2 Molecules

    Victor F. Seabra, George Thomas, Bertrand L. Jaber
    American Journal of Kidney Diseases December 2009 (Vol. 54, Issue 6, Pages 990-992)

American Journal of Kidney Diseases
Volume 54, Issue 6 , Pages 1062-1071, December 2009

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