- Email: [email protected]
Factors Involved in Baseline Hyperhomocysteinemia in Renal Transplantation
Factors Involved in Baseline Hyperhomocysteinemia in Renal Transplantation J.M. Dı´az, Z. Sainz, I. Gich, L.L. Guirado, T. Puig, A. Oliver, R. Montañés, E. Chuy, and R. Solà ABSTRACT Hyperhomocysteinemia (hyperHcy) is one cardiovascular risk. The objective of this study was to establish the prevalence demographic, and clinical and analytical factors related to hyperhomocysteinemia among renal transplant patients. The mean Hcy level was 17.3 mol/L; the prevalence of hyperHcy was 61.2%. The population was categorized as hyperHcy and normal-homocysteinemia (Hcy) patients. Those subjects with hyperHcy were mostly men, with lower intraerythrocyte folate and vitamin B12 levels, higher fibrinogen levels, and poorer renal function. Multivariate evaluation showed that creatinine clearance, plasma intraerythrocyte folate and vitamin B12 levels, and plasma fibrinogen levels were independently associated with Hcy levels. Even though the Hcy level was slightly higher among patients who suffered a posttransplantation cardiovascular event, this was statistically significant.
S
URVIVAL OF RENAL grafts has progressively increased over the last few years. The most frequent causes of renal graft loss are death of the patient with a functional graft (basically cardiovascular in etiology) and chronic graft nephropathy.1 In addition to the well-known factors of cardiovascular risk (diabetes, hypertension, dyslipidemia, and smoking habit), other aspects are gaining increasing importance, particularly hyperhomocysteinemia (hyperHcy).2 HyperHcy is one factor of cardiovascular risk in the general population, which has been associated with coronary mortality.3 Some studies have shown an inverse relationship between homocysteine levels and the degree of renal function.4 However, data on prevalence, predisposing factors and prognosis of hyperHcy in patients with renal transplants are sparse and inconclusive.5,6 The objective of this study was to establish the prevalence, demographics, and clinical and analytical factors related to hyperHcy in stable patients with renal transplants, and to assess whether patients with hyperHcy were more prone to a cardiovascular event. PATIENTS AND METHODS In this observational, prospective analysis we studied 209 patients with renal transplants (139 men [66.5%] and 70 women [33.5%]) of mean age 52 years (standard deviation [SD] 13.8), carrying a functional graft for over 1 year and with a mean posttransplantation follow-up of 5 years. The data set included demographics, posttransplantation atherosclerotic cardiovascular diseases, and factors influencing homocysteine metabolism.
To avoid interference with other data (homocysteinemia (Hcy), intraerythrocyte folate, and vitamin B12 levels), none of the patients was receiving treatment with either folic acid or vitamin B complex. The technology to determine Hcy, vitamin B12, and folate plasma levels was chemoluminescence. HyperHcy has been defined as plasma homocysteine levels greater than 15 mol/L. Continuous variables were expressed as mean values with SDs between brackets. For categorical variables the results were expressed as percentages. Chi-square and Student t tests were used in bivariate studies. A stepwise multivariate study was performed with logistic regression with creatinine clearance chosen as the indicator of the renal function, since there was colinearity with plasma creatinine). Significance was considered when P ⬍ .05.
RESULTS
The mean Hcy level of the entire population was 17.3 mol/L (6.7, 0.7 to 37.1) with intraerythrocyte folate levels of 426 nmol/L (299, 62 to 1754) and vitamin B12 levels of 350 pmol/L (152, 112 to 1600). The prevalence of hyperhomocysteinemia was 61.2% (95% confidence interval [CI] From the Renal Transplantation Unit (J.M.D., Z.S., L.L.G., E.C., R.S.), Nephrology Department, Fundació Puigvert; Epidemiology Department (J.G., T.P.), Hospital de la Santa Creu i Sant Pau; and Laboratory Service (A.O., R.M.), Fundació Puigverts Universitat Autónoma Barcelona, Barcelona, Spain. Address reprint requests to J.M. Dı´az, Renal Transplantation Unit, Nephrology Department, Fundació Puigverts Universitat Autónoma Barcelona, Cartagena, 340.08025 Barcelona, Spain. E-mail: [email protected]
© 2005 by Elsevier Inc. All rights reserved. 360 Park Avenue South, New York, NY 10010-1710
0041-1345/05/$–see front matter doi:10.1016/j.transproceed.2005.10.056
Transplantation Proceedings, 37, 3799 –3801 (2005)
3799
3800
DÍAZ, SAINZ, GICH ET AL Table 1. Results According to Categorized Homocysteine (n ⴝ 209) Univariate study
Age (y) Gender (men) Folic (nmol/L) B12 (pmol/L) Fibrinogen (g/L) CRP (mg/L) Albumin (g/L) Creatinine (mol/L) Creatinine clearance (mL/min) Proteinuria ⬎ 0.3 g/day
Multivariate study
Normal Hcy
HyperHcy
P
47.4 (11.9) 55% 475 (342) 379 (192) 3.48 (0.97) 4.22 (5) 42.7 (3.6) 112 (34) 72 (23) 18.8%
54.2 (14.3) 73.6% 396 (266) 332 (118) 3.92 (0.93) 5.9 (10.1) 43 (3.7) 166 (67) 50 (22) 40.6%
⬍.001 .04 .062 .029 .004 .2 .45 ⬍.001 ⬍.001 .001
Coef. B
0.837 ⫺0.002 ⫺0.003 0.478
⫺0.001
P
NS .037 .005 .04 .019 NS NS Co ⬍.001 NS
OR
95% CI OR
2.309 0.998 0.997 1.612
1.052–5.067 0.997–0.999 0.994–1.000 1.082–2.403
0.954
0.937–0.971
Co, colinearity with creatinine clearance.
54.6 to 67.8). Within the group of patients with hyperHcy, most (91%) presented with moderate hyperHcy (15 to 30 mol/L levels), whereas only 9% had levels higher than 30 mol/L. Once the population was categorized according to Hcy levels those with hyperHcy were mostly men, mostly aged, having lower intraerythrocyte folate and vitamin B12 levels, higher fibrinogen levels, and poorer renal function (Table 1). No relationship was found with the other parameters: smoking habit, diabetes, arterial hypertension, dyslipidemia, albuminemia, or C-reactive protein. Even though the Hcy level was slightly higher among patients receiving cyclosporine compared to those receiving tacrolimus (17.8 mol/L vs 17.1 mol/L), the difference was not statistically significant (P ⫽ .39). Multivariate evaluation showed that creatinine clearance, plasma intraerythrocyte folate and vitamin B12 levels, as well as plasma fibrinogen level were independently associated with the Hcy level (Table 1). Since glomerular filtration is a significant factor, when we grouped the population over the base of their renal function applying the current K/DOKI (Kidney Disease Outcome Quality Initiative) definitions (Table 2), we observed a progressive increase in Hcy at the stages of chronic renal disease (stage 1: 12.5 mol/L; stage 2: 14.5 mol/L; stage 3: 18.1 mol/L; stage 4: 25.4 mol/L). However, a filtration rate below 60 mL/min was basically the one at which the differences were more noticeable, since there were no differences between patients in stages 1 and 2 but there were between these two groups and patients in stages 3 and 4. Following renal transplantation and prior to Hcy baseline Table 2. Hcy Levels in Stages of Chronic Kidney Diseases Stage
Glomerular filtration (mL/min)
n
1 2 3 4 5
⬎90 60–89 30–59 15–29 ⬍15
17 72 95 25 0
Homocysteine (mol/L)
12.5 (SD 4.7) 14.5 (SD 5.2) 18.1 (SD 6.0) 25.4 (SD 6.0)
P ⬍ .001 intergroups, except nonsignificant (.168) between stages 1 and 2.
determination, 16% of the patients had experienced a nonfatal cardiovascular event. The Hcy level was slightly but not significantly higher among patients who suffered a posttransplantation cardiovascular event (18.6 mol/L vs 16.9 mol/L); (P ⫽ .195). DISCUSSION
HyperHcy prevalence in our study was 61.2%, but usually the extent was moderate since only approximately 5% of patients showed Hcy levels higher than 30 mol/L. Other studies have noted similar results.7 The Hcy level was not associated with the albumin level in our study, probably because most of our patients did not suffer from hypoalbuminemia. As happens with other groups,8 we have not been able to show an independent association between hyperHcy and CRP. We have found significantly increased plasma fibrinogen levels among patients with hyperHcy—the clinical significance of which needs to be elucidated. Even though one study found differences according to the type of anticalcineurin therapy,9 we did not confirm this, perhaps because, in contrast to that study, the plasma creatinine values in our study were similar among cyclosporine- versus tacrolimustreated patients. As can be inferred from the multivariate analysis, Hcy patients display poorer renal function, lower plasma intraerythrocyte folate and vitamin B12 levels, and higher plasma fibrinogen levels. Glomerular filtration was the most powerful independent variable. These data agree with other studies4,7 that also suggest that the vitamin status has less impact on Hcy than renal function. The results obtained upon categorizing patients according to their renal function suggest that it is reasonable to determine Hcy in those patients with creatinine clearances below 60 mL/min. Although those patients who had experienced a nonfatal cardiovascular event had higher Hcy levels, the difference was not statistically significant. Among the general population, a moderate Hcy increase is a cardiovascular risk factor.8 The studies suggesting that hyperHcy may be a cardiovascular risk factor in renal transplantation are sparse; however, one trial7 showed that patients with a
FACTORS IN HYPERHOMOCYSTEINEMIA
cardiovascular event (including death) had higher Hcy levels, even though the mean levels were 21.2 mol/L (ie, higher than those in our study). The authors of the abovementioned trial reported a 6% increase in cardiovascular disease with each mol/L Hcy increase. In conclusion, the prevalence of hyperHcy in renal transplantation was 61.2% (95% CI 51.6 to 67.8). The Hcy plasma levels significantly depended upon the gender, the degree of renal function, as well as the plasma folate and vitamin B12 and fibrinogen levels. Hyperhomocysteinemic patients have a poorer renal function, lower folate and vitamin B12 levels, and higher plasma fibrinogen levels. REFERENCES 1. U.S. Renal Data System: USRDS 2000, Annual Report, 2000 2. Kasiske BL: Epidemiology of cardiovascular disease after renal transplantation. Transplantation 72:S5, 2001 3. Schnyder G, Roffi M, Flammer Y, et al: Effect of homocysteinelowering therapy with folic acid, vitamin B12 and vitamin B6 on clinical
3801 outcome after percutaneous coronary intervention. JAMA 288:973, 2002 4. Friedman A, Bostom A, Selhub J, et al: The kidney and homocysteine metabolism. J Am Soc Nephrol 12:2181, 2001 5. Ducloux D, Ruedin C, Gibey R, et al: Prevalence, determinants, and clinical significance of hyperhomocysteinemia in renaltransplantation recipients. Nephrol Dial Transplant 13:2890, 1998 6. Arnadottir M, Hultberg B, Wahlberg J, et al: Serum total homocysteine concentration before and after renal transplantation. Kidney Int 54:1380, 1998 7. Ducloux D, Motte G, Challier B, et al: Serum total homocysteine and cardiovascular disease occurrence in chronic, stable renal transplantation recipients: a prospective study. J Am Soc Nephrol 11:134, 2000 8. Suliman M, Stenvinkel P, Barany P, et al: Hyperhomocysteine and its relationship to cardiovascular disease in ESRD: influence of hypoalbuminemia, malnutrition, inflammation, and diabetes mellitus. Am J Kidney Dis 41(Suppl 1):89, 2003 9. Laurés AS, Gómez E, Alvarez V, et al: Influence of anticalcineurinic therapy in plasma homocysteine levels of renal transplantation recipients. Transplant Proc 35:1739, 2003
S
URVIVAL OF RENAL grafts has progressively increased over the last few years. The most frequent causes of renal graft loss are death of the patient with a functional graft (basically cardiovascular in etiology) and chronic graft nephropathy.1 In addition to the well-known factors of cardiovascular risk (diabetes, hypertension, dyslipidemia, and smoking habit), other aspects are gaining increasing importance, particularly hyperhomocysteinemia (hyperHcy).2 HyperHcy is one factor of cardiovascular risk in the general population, which has been associated with coronary mortality.3 Some studies have shown an inverse relationship between homocysteine levels and the degree of renal function.4 However, data on prevalence, predisposing factors and prognosis of hyperHcy in patients with renal transplants are sparse and inconclusive.5,6 The objective of this study was to establish the prevalence, demographics, and clinical and analytical factors related to hyperHcy in stable patients with renal transplants, and to assess whether patients with hyperHcy were more prone to a cardiovascular event. PATIENTS AND METHODS In this observational, prospective analysis we studied 209 patients with renal transplants (139 men [66.5%] and 70 women [33.5%]) of mean age 52 years (standard deviation [SD] 13.8), carrying a functional graft for over 1 year and with a mean posttransplantation follow-up of 5 years. The data set included demographics, posttransplantation atherosclerotic cardiovascular diseases, and factors influencing homocysteine metabolism.
To avoid interference with other data (homocysteinemia (Hcy), intraerythrocyte folate, and vitamin B12 levels), none of the patients was receiving treatment with either folic acid or vitamin B complex. The technology to determine Hcy, vitamin B12, and folate plasma levels was chemoluminescence. HyperHcy has been defined as plasma homocysteine levels greater than 15 mol/L. Continuous variables were expressed as mean values with SDs between brackets. For categorical variables the results were expressed as percentages. Chi-square and Student t tests were used in bivariate studies. A stepwise multivariate study was performed with logistic regression with creatinine clearance chosen as the indicator of the renal function, since there was colinearity with plasma creatinine). Significance was considered when P ⬍ .05.
RESULTS
The mean Hcy level of the entire population was 17.3 mol/L (6.7, 0.7 to 37.1) with intraerythrocyte folate levels of 426 nmol/L (299, 62 to 1754) and vitamin B12 levels of 350 pmol/L (152, 112 to 1600). The prevalence of hyperhomocysteinemia was 61.2% (95% confidence interval [CI] From the Renal Transplantation Unit (J.M.D., Z.S., L.L.G., E.C., R.S.), Nephrology Department, Fundació Puigvert; Epidemiology Department (J.G., T.P.), Hospital de la Santa Creu i Sant Pau; and Laboratory Service (A.O., R.M.), Fundació Puigverts Universitat Autónoma Barcelona, Barcelona, Spain. Address reprint requests to J.M. Dı´az, Renal Transplantation Unit, Nephrology Department, Fundació Puigverts Universitat Autónoma Barcelona, Cartagena, 340.08025 Barcelona, Spain. E-mail: [email protected]
© 2005 by Elsevier Inc. All rights reserved. 360 Park Avenue South, New York, NY 10010-1710
0041-1345/05/$–see front matter doi:10.1016/j.transproceed.2005.10.056
Transplantation Proceedings, 37, 3799 –3801 (2005)
3799
3800
DÍAZ, SAINZ, GICH ET AL Table 1. Results According to Categorized Homocysteine (n ⴝ 209) Univariate study
Age (y) Gender (men) Folic (nmol/L) B12 (pmol/L) Fibrinogen (g/L) CRP (mg/L) Albumin (g/L) Creatinine (mol/L) Creatinine clearance (mL/min) Proteinuria ⬎ 0.3 g/day
Multivariate study
Normal Hcy
HyperHcy
P
47.4 (11.9) 55% 475 (342) 379 (192) 3.48 (0.97) 4.22 (5) 42.7 (3.6) 112 (34) 72 (23) 18.8%
54.2 (14.3) 73.6% 396 (266) 332 (118) 3.92 (0.93) 5.9 (10.1) 43 (3.7) 166 (67) 50 (22) 40.6%
⬍.001 .04 .062 .029 .004 .2 .45 ⬍.001 ⬍.001 .001
Coef. B
0.837 ⫺0.002 ⫺0.003 0.478
⫺0.001
P
NS .037 .005 .04 .019 NS NS Co ⬍.001 NS
OR
95% CI OR
2.309 0.998 0.997 1.612
1.052–5.067 0.997–0.999 0.994–1.000 1.082–2.403
0.954
0.937–0.971
Co, colinearity with creatinine clearance.
54.6 to 67.8). Within the group of patients with hyperHcy, most (91%) presented with moderate hyperHcy (15 to 30 mol/L levels), whereas only 9% had levels higher than 30 mol/L. Once the population was categorized according to Hcy levels those with hyperHcy were mostly men, mostly aged, having lower intraerythrocyte folate and vitamin B12 levels, higher fibrinogen levels, and poorer renal function (Table 1). No relationship was found with the other parameters: smoking habit, diabetes, arterial hypertension, dyslipidemia, albuminemia, or C-reactive protein. Even though the Hcy level was slightly higher among patients receiving cyclosporine compared to those receiving tacrolimus (17.8 mol/L vs 17.1 mol/L), the difference was not statistically significant (P ⫽ .39). Multivariate evaluation showed that creatinine clearance, plasma intraerythrocyte folate and vitamin B12 levels, as well as plasma fibrinogen level were independently associated with the Hcy level (Table 1). Since glomerular filtration is a significant factor, when we grouped the population over the base of their renal function applying the current K/DOKI (Kidney Disease Outcome Quality Initiative) definitions (Table 2), we observed a progressive increase in Hcy at the stages of chronic renal disease (stage 1: 12.5 mol/L; stage 2: 14.5 mol/L; stage 3: 18.1 mol/L; stage 4: 25.4 mol/L). However, a filtration rate below 60 mL/min was basically the one at which the differences were more noticeable, since there were no differences between patients in stages 1 and 2 but there were between these two groups and patients in stages 3 and 4. Following renal transplantation and prior to Hcy baseline Table 2. Hcy Levels in Stages of Chronic Kidney Diseases Stage
Glomerular filtration (mL/min)
n
1 2 3 4 5
⬎90 60–89 30–59 15–29 ⬍15
17 72 95 25 0
Homocysteine (mol/L)
12.5 (SD 4.7) 14.5 (SD 5.2) 18.1 (SD 6.0) 25.4 (SD 6.0)
P ⬍ .001 intergroups, except nonsignificant (.168) between stages 1 and 2.
determination, 16% of the patients had experienced a nonfatal cardiovascular event. The Hcy level was slightly but not significantly higher among patients who suffered a posttransplantation cardiovascular event (18.6 mol/L vs 16.9 mol/L); (P ⫽ .195). DISCUSSION
HyperHcy prevalence in our study was 61.2%, but usually the extent was moderate since only approximately 5% of patients showed Hcy levels higher than 30 mol/L. Other studies have noted similar results.7 The Hcy level was not associated with the albumin level in our study, probably because most of our patients did not suffer from hypoalbuminemia. As happens with other groups,8 we have not been able to show an independent association between hyperHcy and CRP. We have found significantly increased plasma fibrinogen levels among patients with hyperHcy—the clinical significance of which needs to be elucidated. Even though one study found differences according to the type of anticalcineurin therapy,9 we did not confirm this, perhaps because, in contrast to that study, the plasma creatinine values in our study were similar among cyclosporine- versus tacrolimustreated patients. As can be inferred from the multivariate analysis, Hcy patients display poorer renal function, lower plasma intraerythrocyte folate and vitamin B12 levels, and higher plasma fibrinogen levels. Glomerular filtration was the most powerful independent variable. These data agree with other studies4,7 that also suggest that the vitamin status has less impact on Hcy than renal function. The results obtained upon categorizing patients according to their renal function suggest that it is reasonable to determine Hcy in those patients with creatinine clearances below 60 mL/min. Although those patients who had experienced a nonfatal cardiovascular event had higher Hcy levels, the difference was not statistically significant. Among the general population, a moderate Hcy increase is a cardiovascular risk factor.8 The studies suggesting that hyperHcy may be a cardiovascular risk factor in renal transplantation are sparse; however, one trial7 showed that patients with a
FACTORS IN HYPERHOMOCYSTEINEMIA
cardiovascular event (including death) had higher Hcy levels, even though the mean levels were 21.2 mol/L (ie, higher than those in our study). The authors of the abovementioned trial reported a 6% increase in cardiovascular disease with each mol/L Hcy increase. In conclusion, the prevalence of hyperHcy in renal transplantation was 61.2% (95% CI 51.6 to 67.8). The Hcy plasma levels significantly depended upon the gender, the degree of renal function, as well as the plasma folate and vitamin B12 and fibrinogen levels. Hyperhomocysteinemic patients have a poorer renal function, lower folate and vitamin B12 levels, and higher plasma fibrinogen levels. REFERENCES 1. U.S. Renal Data System: USRDS 2000, Annual Report, 2000 2. Kasiske BL: Epidemiology of cardiovascular disease after renal transplantation. Transplantation 72:S5, 2001 3. Schnyder G, Roffi M, Flammer Y, et al: Effect of homocysteinelowering therapy with folic acid, vitamin B12 and vitamin B6 on clinical
3801 outcome after percutaneous coronary intervention. JAMA 288:973, 2002 4. Friedman A, Bostom A, Selhub J, et al: The kidney and homocysteine metabolism. J Am Soc Nephrol 12:2181, 2001 5. Ducloux D, Ruedin C, Gibey R, et al: Prevalence, determinants, and clinical significance of hyperhomocysteinemia in renaltransplantation recipients. Nephrol Dial Transplant 13:2890, 1998 6. Arnadottir M, Hultberg B, Wahlberg J, et al: Serum total homocysteine concentration before and after renal transplantation. Kidney Int 54:1380, 1998 7. Ducloux D, Motte G, Challier B, et al: Serum total homocysteine and cardiovascular disease occurrence in chronic, stable renal transplantation recipients: a prospective study. J Am Soc Nephrol 11:134, 2000 8. Suliman M, Stenvinkel P, Barany P, et al: Hyperhomocysteine and its relationship to cardiovascular disease in ESRD: influence of hypoalbuminemia, malnutrition, inflammation, and diabetes mellitus. Am J Kidney Dis 41(Suppl 1):89, 2003 9. Laurés AS, Gómez E, Alvarez V, et al: Influence of anticalcineurinic therapy in plasma homocysteine levels of renal transplantation recipients. Transplant Proc 35:1739, 2003