Summary
Background and objectives
Persistent inflammation and oxidative stress play a pathogenic role in the high cardiovascular morbidity and mortality of hemodialysis patients. Heme oxygenase-1 is considered to have anti-inflammatory and antioxidant properties. This study assessed the association between the length of guanosine thymidine dinucleotide repeats in the heme oxygenase-1 gene microsatellite promoter and cardiovascular events and mortality among hemodialysis patients.
Design, setting, participants, & measurements
Study participants were recruited from October 1, 2006 to December 31, 2006. The allelic frequencies of the length of guanosine thymidine dinucleotide repeats (the S allele represents shorter [<27] repeats, and the L allele represents longer [≥27] repeats) in the heme oxygenase-1 gene promoter were analyzed in 1080 unrelated chronic hemodialysis patients and 365 healthy controls for distribution comparison. Cardiovascular events and mortality were the study outcomes, and the hemodialysis patients were followed until June 30, 2011.
Results
The genotype proportions were 20.6%, 48.8%, and 30.6% for S/S, S/L, and L/L, respectively, in the hemodialysis patients and comparable with those proportions in healthy controls. The patients with the L/L genotype had significantly higher baseline serum high-sensitivity C-reactive protein and malondialdehyde levels than the patients with the S/S or S/L genotypes. During a median follow-up of 50 months, 307 patients died. A Kaplan–Meier survival analysis showed the highest cardiovascular events and all-cause mortality in patients with the L/L genotype. The adjusted hazard ratios (95% confidence intervals) for each L allele in additive model were 1.42 (1.20 to 1.67 [P<0.001]) for cardiovascular events and 1.19 (1.01 to 1.40 [P=0.03]) for all-cause mortality.
Conclusions
Chronic hemodialysis patients with longer lengths of guanosine thymidine dinucleotide repeats in the heme oxygenase-1 gene promoter exhibit higher inflammation and oxidative stress. These patients have higher risk of long-term cardiovascular events and mortality.
Introduction
Cardiovascular disease (CVD) is the major cause of death among the hemodialysis (HD) population (1). In addition to a high prevalence of traditional cardiovascular (CV) risk factors, the presence of chronic inflammation and oxidative stress is thought to play a pathogenic role in the development of CVD among chronic dialysis patients (2).
Heme oxygenase (HO) is the rate-limiting enzyme in heme degradation. The enzyme generates free iron, biliverdin, and carbon monoxide. Biliverdin is subsequently converted to bilirubin by biliverdin reductase, and free iron is rapidly sequestered by ferritin (3). HO is a cytoprotective enzyme that potentially exerts antioxidant, anti-inflammatory, antiapoptotic, and angiogenic functions through its reactive products (4). HO-1 is the inducible isoform, whereas HO-2 expresses constitutively. HO-1 expresses in various tissues and is upregulated by cellular stress. Cumulative experimental evidence supports HO-1 as a key protective component in various CVD processes (5).
The human HO-1 gene has been mapped to chromosome 22q12 (6), and the number of guanosine thymidine dinucleotide repeats [(GT)n] in the HO-1 gene microsatellite promoter is inversely associated with HO-1 mRNA levels and enzyme activity (7). An increased susceptibility to CV events and increased mortality of longer (GT)n in the HO-1 gene promoter have been reported in high-risk patients with coronary heart disease (CHD), hypercholesterolemia, diabetes mellitus, history of smoking, peripheral artery disease, or arsenic exposure (7–11). A previous study has proposed that longer (GT)n in the HO-1 promoter predicted a higher frequency of arteriovenous fistula failure and a poorer arteriovenous fistula patency in HD patients (12). However, information about the association between the length polymorphism in HO-1 promoter and hard end points in HD patients is scarce. We postulate that HO-1 may be protective against CVD and mortality among patients undergoing HD. This study aims to investigate whether the length polymorphism of the (GT)n in the HO-1 promoter is an independent predictor of CV events and all-cause mortality in chronic HD patients.
Materials and Methods
Research Population
This prospective cohort study was conducted at nine dialysis centers in the Taipei metropolitan area. Study participants were recruited from October 1 to December 31, 2006. Initially, all patients undergoing HD were screened. A total of 1151 patients who were older than 20 years of age and had an HD vintage of more than 6 months before the study was included. Exclusion criteria were weekly dialysis for less than 12 hours (n=6); inadequacy of dialysis, with urea Kt/V of less than 1.2 (n=10); and conditions of malignancy (n=15), infectious disease or sepsis (n=5), and hepatobiliary disease (n=35). Finally, 1080 clinically stable patients were enrolled (552 men and 528 women; mean age=59 years). All patients received a standard bicarbonate dialysis session. The median duration of HD before the study was 52 months. A group of 365 healthy controls (190 men and 175 women; mean age=57 years) was recruited from volunteers who were receiving health checkups. The healthy controls were enrolled for genotyping of the length polymorphism of (GT)n in the HO-1 gene promoter. They had normal renal function, which was defined on the basis of an estimated GFR value using a simplified Modifications of Diet in Renal Disease equation of greater than 100 ml/min per 1.73 m2 (13). The healthy volunteers had no risk factors of CVDs or health issues that may increase risk of kidney disease. The study protocol was approved by the institutional review board of each affiliated hospital. Informed consent was obtained from all participants, and our study complies with the Declaration of Helsinki. In this study, all the study participants were Taiwanese and had similar ethnic backgrounds. Therefore, statistical artifacts caused by population stratification could be ruled out as described by Pritchard and Rosenberg (14).
Clinical Data Collection
Baseline demographic data were recorded at the time of recruitment. Diabetes was diagnosed on the basis of the World Health Organization criteria. Hypertension was defined as a measured systolic BP greater than 140 mmHg, a diastolic BP greater than 90 mmHg, and/or use of antihypertensive medications. The presence of CVD was defined as a medical history and clinical findings of congestive heart failure and coronary artery, cerebrovascular, and/or peripheral vascular disease. These data were complemented by clinical assessments of body weight, body mass index, and BP. The predialysis BP was measured by an automated sphygmomanometer in the nonaccess arm after a 5-minute rest with the patient in the sitting position with both feet on the floor.
Laboratory Measurements
Venous blood samples were drawn from fasting healthy individuals or HD patients who had fasted overnight before the start of a midweek dialysis session before administering heparin. Albumin was measured using the bromocresol green method. Iron, total cholesterol, triglyceride, HDL cholesterol, LDL cholesterol, urea, and creatinine in the serum were determined using commercial kits and a Hitachi 7600 autoanalyzer (Roche Modular; Hitachi Ltd., Tokyo, Japan). The total iron binding capacity (TIBC) was measured using the TIBC Microtest (Daiichi, Tokyo, Japan), and serum ferritin was determined using an RIA (Incstar, Stillwater, MN). Transferrin saturation was calculated as the ratio of serum iron to TIBC and presented as percentages. Serum high-sensitivity C-reactive protein (hs-CRP) was measured by an immunoturbidimetric assay using rate nephelometry (IMMAGE; Beckman Coulter, Galway, Ireland). Plasma malondialdehyde was determined with a thiobarbituric acid test. The adducts consisting of two molecules of thiobarbituric acid were separated by the HPLC method described by Nielsen et al. (15). The adequacy of dialysis was estimated by measuring the midweek urea clearance (Kt/V) using the standard method (16).
Length Polymorphism of (GT)n in the HO-1 Gene Promoter
Genomic DNAs were extracted from leukocytes with conventional procedures. The 5′-flanking region containing (GT)n of the HO-1 gene was amplified by the PCR with a fluorescein amidite-labeled sense primer, 5′-AGAGCCTGCAGCTTCTCAGA-3′, and an antisense primer, 5′-ACAAAGTCTGGCCATAGGAC-3′, according to the published procedure (17). The PCR products were mixed together with the GenoType TAMRA DNA ladder (size range=50–500 bp; GibcoBRL) and analyzed with an automated DNA sequencer (ABI Prism 377). Each size of the (GT)n was calculated with GeneScan analysis software (PE Applied Biosystems). This study selected 27 GT repeats as a cutoff to classify the participants for allele typing; the proportion of allele frequencies with less than 27 GT repeats was approximately 50%, and the cutoff value was consistent with the previously published literature (9,11,18). Thus, short repeats with less than 27 GT repeats were designated as S alleles, and long repeats with at least 27 GT repeats were designated as L alleles. According to each of their HO-1 promoter alleles, the participants were categorized into L/L, L/S, or S/S genotypes.
Outcome Data Collection
The primary outcome measures were CV events and all-cause mortality from the time of inclusion in the study. The cohort was followed until June 30, 2011. A trained physician who was blinded to the length polymorphism of (GT)n in the HO-1 gene promoter independently obtained information about the occurrence of interim CV events and cause of death by reviewing hospital records and making phone calls to the study patients. For the patients transferred to other dialysis units, they were also followed using the questionnaire forms, which were completed by the attending physicians in the other units. The composite CV events included fatal and nonfatal myocardial infarction and stroke, congestive heart failure, peripheral artery disease, and sudden death. The all-cause mortality included death related to CV events, infection, sepsis, malignancy, gastrointestinal bleeding, chronic obstructive lung disease, and cachexia.
Statistical Analyses
Comparisons of the genotypes and the allelic frequencies of the HO-1 microsatellite promoter polymorphism between the HD patients and the healthy individuals and among the patients with short, moderate, and long dialysis vintages were performed using a chi-squared test. Baseline descriptive variables were expressed as percentages for categorical data, means and SDs for continuous data with a normal distribution, and medians and interquartile ranges for continuous data without a normal distribution. Potential differences among the three patient groups of the HO-1 promoter genotype were assessed with ANOVA for normally distributed data, the Kruskal–Wallis test for non-normally distributed data, or the Pearson chi-squared test for categorical variables. Before commencing the study, a sample size calculation was performed, in which the statistical power was 90% and the 5-year survival rate was 53.7% among the Taiwan dialysis population (19). Intergroup difference would be reflected by a hazard ratio of at least 1.6. The required sample size in our study was, thus, estimated at 985 or more patients. Therefore, a total of 1080 patients recruited in the study fulfilled the minimal requirement of case number. Cumulative survival curves for the CV events and all-cause mortality were generated using the Kaplan–Meier method. Between-group survival rates among the genotypes of the HO-1 promoter polymorphism were compared using a log-rank test. A multivariate Cox regression model was used to estimate the hazard ratios of composite CV events and all-cause mortality in relation to the genotypes of the HO-1 microsatellite promoter polymorphism. The analysis was adjusted for age, sex, smoking status, diabetes, prior CVD, body mass index, total cholesterol, systolic BP, HD duration, urea Kt/V, serum albumin, and hemoglobin. Because the length polymorphism in HO-1 promoter was significantly associated with hs-CRP and malondialdehyde, these three variables were not offered simultaneously in a Cox regression model to avoid multicollinearity. Statistical analyses were performed using the computer software SPSS version 16.0 (SPSS Inc., Chicago, IL). All P values were two-tailed. P values less than 0.05 were considered statistically significant.
Results
Length Polymorphism of (GT)n in the HO-1 Gene Promoter
Figure 1A shows the frequency distribution of (GT)n of the HO-1 promoter in the 1080 HD patients and 365 healthy controls. The allelic distribution ranged from 16 to 39 GT repeats, with 23 and 30 GT repeats being the two most common alleles. Our data corroborate previous observations (8,11,20). The genotype proportions and L-allelic frequencies of the HO-1 microsatellite promoter polymorphism in HD patients were comparable with the genotype proportions and L-allelic frequencies in healthy controls (Table 1), and Hardy–Weinberg equilibrium was met. Because all HD patients were prevalent patients, we also stratified them into three groups according to their dialysis vintage. Again, the genotype distributions and L-allelic frequencies were not different among the three groups (Table 1).
Figure 1.
Frequency distribution of the number of guanosine thymidine dinucleotide repeats [(GT)n] of the heme oxygenase-1 microsatellite promoter. (A) There are 1080 hemodialysis patients and 365 healthy controls. The (GT)n ranges from 16 to 39. There is a bimodal distribution with one peak located at 23 repeats and one peak located at 30 repeats in both groups. The frequency distributions of (GT)n are not significantly different between the hemodialysis patients and the healthy controls. (B) The frequency distributions of (GT)n are not significantly different between the 85 censored and 995 noncensored patients (P=0.16 by Pearson chi-squared test).
Table 1.
Genotype and allelic frequency of heme oxygenase-1 (HO-1) microsatellite promoter polymorphism in healthy controls and hemodialysis patients grouped by hemodialysis vintage
| Parameters | Healthy Controls (n=365) | Hemodialysis Patients | |||
|---|---|---|---|---|---|
| Total (n=1080) | Hemodialysis Duration (mo) | ||||
| ≤32 (n=360) | 33–82 (n=365) | ≥83 (n=355) | |||
| Genotype | |||||
| S/S, n (%) | 79 (21.6) | 223 (20.6) | 71 (19.7) | 70 (19.2) | 82 (23.1) |
| S/L, n (%) | 196 (53.7) | 526 (48.8) | 178 (49.4) | 186 (51.0) | 162 (45.6) |
| L/L, n (%) | 90 (24.7) | 331 (30.6) | 111 (30.8) | 109 (29.9) | 111 (31.3) |
| L-allelic frequency | 0.52 | 0.55 | 0.56 | 0.55 | 0.54 |
S allele, number of guanosine thymidine dinucleotide repeats [(GT)n]<27; L allele, (GT)n≥27.
Inflammation and Oxidative Stress
The baseline demographic characteristics and traditional and dialysis-related risk factors of the study population stratified by the HO-1 promoter polymorphism genotype are presented in Table 2. Serum hs-CRP and plasma malondialdehyde levels were highest in patients with the L/L genotype, intermediate in patients with the S/L genotype, and lowest in patients with the S/S genotype (Figure 2). The results suggested that the L/L genotype was associated with higher inflammation and oxidative stress.
Table 2.
Baseline demographic and laboratory characteristics of hemodialysis patients stratified by genotypes of heme oxygenase-1 (HO-1) microsatellite promoter polymorphism
| Parameters | All Patients (n=1080) | HO-1 Promoter Genotype | |||
|---|---|---|---|---|---|
| S/S (n=223) | S/L (n=526) | L/L (n=331) | P Value | ||
| Age, yr | 59±14 | 58±15 | 58±14 | 60±13 | 0.01 |
| Men, n (%) | 552 (51.1) | 112 (50.2) | 257 (48.8) | 183 (55.3) | 0.88 |
| Current smoker, n (%) | 331 (30.6) | 67 (30.0) | 181 (34.4) | 83 (25.1) | 0.63 |
| Hypertension, n (%) | 620 (57.4) | 120 (53.8) | 300 (57.0) | 200 (60.4) | 0.89 |
| Diabetes mellitus, n (%) | 338 (31.3) | 70 (31.4) | 160 (30.4) | 108 (32.6) | 0.95 |
| Previous cardiovascular disease, n (%) | 317 (29.3) | 59 (26.4) | 216 (29.8) | 101 (30.5) | 0.50 |
| Body mass index, kg/m2 | 21.9±3.2 | 21.5±3.0 | 21.9±3.3 | 22.0±3.5 | 0.62 |
| Systolic BP, mmHg | 139±22 | 132±23 | 142±30 | 139±22 | 0.54 |
| Diastolic BP, mmHg | 78±11 | 77±10 | 78±12 | 78±10 | 0.79 |
| Hemodialysis duration, mo | 52 (25, 103) | 58 (26, 105) | 49 (25, 97) | 54 (26, 105) | 0.44 |
| Kt/V urea | 1.83±0.51 | 1.83±0.47 | 1.80±0.39 | 1.86±0.69 | 0.26 |
| Total cholesterol, mg/dl | 172±36 | 171±34 | 172±39 | 173±41 | 0.80 |
| Triglyceride, mg/dl | 162±115 | 160±109 | 164±119 | 157±102 | 0.69 |
| HDL cholesterol, mg/dl | 39±11 | 38±12 | 39±11 | 39±11 | 0.79 |
| LDL cholesterol, mg/dl | 112±29 | 109±26 | 112±31 | 115±34 | 0.36 |
| Albumin, g/dl | 3.92±0.35 | 3.90±0.34 | 3.93±0.35 | 3.92±0.35 | 0.90 |
| Hemoglobin, g/dl | 10.3±1.5 | 10.7±1.7 | 10.1±1.3 | 10.3±1.5 | 0.71 |
| Dose of epoetin, U/kg per week | 70 (40, 94) | 70 (36, 93) | 70 (40, 95) | 71 (42, 93) | 0.77 |
| Ferritin, μg/L | 361 (200, 607) | 298 (177, 578) | 341 (199, 631) | 365 (208, 669) | 0.31 |
| Transferrin saturation, % | 33±15 | 34±16 | 33±16 | 32±15 | 0.49 |
Figure 2.
Levels of plasma malondialdehyde and high-sensitivity C-reactive protein (CRP) by genotypes. Baseline (A) plasma malondialdehyde and (B) high-sensitivity C-reactive protein in 1080 hemodialysis patients stratified by the genotype of the heme oxygenase-1 (HO-1) microsatellite promoter polymorphism. Whisker plots show the 10th, 25th, 50th, 75th, and 90th percentiles of distribution. aP<0.01 versus S/S genotype. bP<0.05 versus S/L genotype.
CV Events and All-Cause Mortality
During a median follow-up period of 50 months (interquartile range=24–54 months), 73 patients received a kidney transplant, 12 patients were transferred to peritoneal dialysis, and 151 patients were transferred to other dialysis units. The frequency distribution of (GT)n of the HO-1 promoter in the censored patients was similar to the frequency distribution in noncensored patients (Figure 1B). At the end of the follow-up period, 688 patients were confirmed to be alive on HD treatment, and 307 patients had died while being treated. Of the patients who died, 139 (45.3%) patients died from CVD-related causes.
In the Kaplan–Meier analysis curves for end points of CV events and mortality among 1080 HD patients, the risk of CV events was significantly higher in the L/L genotype than in the S/S genotype (P<0.001) and among the S allele noncarriers (L/L genotype) than among the S allele carriers (S/L and S/S genotypes; P<0.001). The risk of all-cause mortality was significantly higher in the L/L genotype than the S/S genotype (P=0.001) and also significantly higher in the S allele noncarriers than the S allele carriers (P=0.005) (Figure 3). The assumption of proportional hazards was confirmed by a log minus log plot and met in the Cox models. Table 3 displays the cumulative CV events and all-cause mortality in the HD patients stratified by the HO-1 promoter genotype during a median follow-up of 50 months. The cumulative CV events were 8.0, 11.4, and 16.9 events per 100 person-years for the S/S, S/L, and L/L genotypes, respectively. The all-cause mortality events were 6.1, 8.6, and 10.9 events per 100 person-years for the S/S, S/L, and L/L genotypes, respectively. The association between the HO-1 promoter genotype and CV events or all-cause mortality was studied through the multivariate Cox regression analysis shown in Table 3. In a recessive model, the S allele noncarriers (L/L genotype) had a significantly higher risk for CV events (adjusted hazard ratio [HR], 1.62; 95% confidence interval [95% CI], 1.28 to 2.04; P<0.001) and a modest risk for death (adjusted HR, 1.22; 95% CI, 0.96 to 1.53; P=0.10) than the S allele carriers (S/L and S/S genotypes). In the additive model, each L allele had significantly higher risks for CV events (adjusted HR, 1.42; 95% CI, 1.20 to 1.67; P<0.001) and death (adjusted HR, 1.19; 95% CI, 1.01 to 1.40; P=0.03).
Figure 3.
Survival curves for the cardiovascular events and all-cause mortality by genotypes. Kaplan–Meier cumulative survival curves for end points of the (A) composite cardiovascular events and (B) all-cause mortality among the 1080 hemodialysis patients in relation to the genotype of the heme oxygenase-1 microsatellite promoter polymorphism. Upper panels are the three genotypes: S/S, S/L, and L/L; lower panels are the genotypes in a recessive model: S/L + S/S and L/L.
Table 3.
Cumulative cardiovascular disease and mortality events and hazard ratios (95% confidence intervals) of genotypes of heme oxygenase-1 (HO-1) microsatellite promoter polymorphism in hemodialysis patients with a median follow-up of 50 months
| Outcomes | Cumulative Events n (events/100 person-yr) by Genotype | Hazard Ratio (95% Confidence Interval) in Cox Regression Models | |||||
|---|---|---|---|---|---|---|---|
| Recessive Model for L/L Versus S/L + S/S | Additive Model for Each L Allele | ||||||
| S/S | S/L | L/L | Crude | Adjusteda | Crude | Adjusteda | |
| Cardiovascular disease | 59 (8.0) | 196 (11.4) | 178 (16.9) | 1.81 (1.44 to 2.28) P<0.001 | 1.62 (1.28 to 2.04) P<0.001 | 1.54 (1.31 to 1.82) P<0.001 | 1.42 (1.20 to 1.67) P<0.001 |
| All-cause mortality | 45 (6.1) | 147 (8.6) | 115 (10.9) | 1.39 (1.11 to 1.76) P=0.01 | 1.22 (0.96 to 1.53) P=0.10 | 1.32 (1.26 to 1.55) P=0.001 | 1.19 (1.01 to 1.40) P=0.03 |
A multivariate Cox regression model was adjusted for age, sex, smoking status, diabetes, prior cardiovascular disease, body mass index, total cholesterol, systolic BP, hemodialysis duration, urea Kt/V, serum albumin, and hemoglobin.
Discussion
This study is the first study in the field of CKD to show that longer (GT)n lengths of the HO-1 promoter are associated with higher risks of future CV events and overall mortality in chronic HD patients. We also found that longer lengths of (GT)n in the HO-1 promoter are associated with higher malondialdehyde and hs-CRP levels. Our data substantiate the previous findings that nonrenal disease patients with longer (GT)n of the HO-1 gene promoter seemed to have higher serum thiobarbituric acid reactive substances (an index of oxidative stress) and higher CRP (an inflammatory marker) (8,20).
Stronger evidence for causality between inflammation/oxidative stress and CVD in CKD may be possible using a Mendelian randomization approach (21). Because S alleles result in higher HO-1 expressions of lifelong persistence, a higher protective effect against CVD from these alleles can be expected. The association between the polymorphism with clinical outcomes is less likely to be influenced by reverse causation or confounding. This finding is in line with our results that the calculated estimate for the association of HO-1 genotype with CVD outcomes changes only marginally after an extended adjustment for other CVD risk factors (Table 3).
The protective effects of HO-1 are thought to be exerted primarily through its reactive products, including carbon monoxide and bilirubin (4,5). Carbon monoxide (22) has vasodilatory, antiproliferative, and anti-inflammatory properties, and bilirubin (23,24) exhibits the antioxidant and anti-inflammatory properties. Although there is no information about HO-1 activity, bilirubin level, or endothelial function in this study, we have found that longer lengths of (GT)n in the HO-1 promoter are associated with higher malondialdehyde and hs-CRP levels. Accordingly, the genotype of the HO-1 gene promoter polymorphism is associated with the risk of CV events and all-cause mortality in HD patients, at least in part, by its anti-inflammatory and antioxidant properties.
In humans, (GT)n lengths have been identified in the proximal promoter region of the HO-1 gene (25). The (GT)n in the HO-1 gene promoter is highly polymorphic and inversely associated with the HO-1 mRNA levels and the enzyme activity (7). Previous human studies revealed that longer (GT)n lengths of the HO-1 gene promoter were associated with higher oxidative stress and inflammation (8,20). The concept that HO-1 may affect the CV outcome in humans has been investigated by studies assessing the (GT)n polymorphism of the HO-1 gene promoter. In two cross-sectional studies with Asian patients, length polymorphism in the HO-1 gene promoter was related to susceptibility for CHD in patients with conventional vascular risk factors, such as diabetes mellitus, hypercholesterolemia, and smoking (8,9). HO-1 promoter polymorphism has been reported to be associated with restenosis after angioplasty intervention (7,20,26). In a longitudinal study, HO-1 promoter polymorphism influenced the occurrence of coronary events in patients with peripheral artery disease (10). Among arsenic-exposed individuals in Taiwan, the carriers of the short (GT)n polymorphisms in the HO-1 gene promoter had lower rates of CV mortality and hypertension and a lower probability of developing carotid atherosclerosis (11,27,28). With regard to ischemic cerebrovascular events, one study reported that patients with long (>26 GT) repeats in the HO-1 gene promoter had greater susceptibility for developing ischemic stroke in the presence of low HDL cholesterol (29). Our finding corroborates the concept that the polymorphism of HO-1 is associated with CVD risk in the high-risk population; patients with CKD, especially ESRD on chronic HD, are definitely a high-risk population for CVD.
This study has some limitations. First, the study patients were prevalent patients instead of incident patients. Because the median HD vintage was 52 months, study patients might represent selected survivors. However, the HO-1 genotype distribution and L-allelic frequency in HD patients were similar to the HO-1 genotype distribution and L-allelic frequency in the healthy controls and showed no difference between censored and noncensored patients or among patients with different dialysis vintage. Thus, the possibility of survivor bias might be low. Second, the findings of our study are applicable to the Taiwanese population, and confirmatory replication studies are needed. Third, other mechanisms of HO-1 may have existed, but we did not have the information about biomarkers other than hs-CRP and malondialdehyde. Finally, because the few event rates limited the analysis, subtype events, like CHD, cerebrovascular disease, and death from a specific cause, were not analyzed.
In summary, this prospective cohort study shows that longer (GT)n lengths of the HO-1 promoter are associated with higher risk of long-term CV events and all-cause mortality among patients undergoing chronic HD. HD patients with the L/L genotype of the HO-1 gene promoter should be treated as having a high risk of CVD and death.
Disclosures
None.
Acknowledgments
We are deeply indebted to Miss P. C. Lee for her expert secretarial assistance and graphic design.
This study was supported by National Science Council Grants NSC 96-2628-B-010-001-MY3 and NSC 99-2314-B-303-002-MY3, Taipei Veterans General Hospital Grant V99C1-121, and a grant from the Ministry of Education’s Aim for the Top University Plan.
Footnotes
Y.-H.C. and S.-C.H. contributed equally to this work.
Published online ahead of print. Publication date available at www.cjasn.org.
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