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Plasma homocysteine levels in renal transplant patients on tacrolimus therapy
Plasma Homocysteine Levels in Renal Transplant Patients on Tacrolimus Therapy S.H. Akbas, M. Tuncer, A. Gurkan, L. Yucetin, A. Yavuz, A. Demirbas, F. Ersoy, M. Gultekin, G. Yakupoglu, and M. Akaydin ABSTRACT Increased plasma total homocysteine levels afford an independent risk factor to assess cardiovascular morbidity in patients with normal and impaired renal function, including stable transplant recipients. The purpose of this study was to evaluate plasma homocysteine levels and factors known to influence homocysteine metabolism (folate and Vitamin B12) in renal transplanted patients treated with tacrolimus. Plasma homocysteine, serum folate and serum vitamin B12 concentrations were measured in 18 cadaveric renal transplant patients with stable function both before and 3 months after the renal transplantation. While the mean plasma homocysteine level in the renal transplant group was significantly higher than in the control group, no significant change was observed following renal transplantation under tacrolimus therapy (16.84 ⫾ 6.43 mol/L vs 16.02 ⫾ 6.54 mol/L). The levels of folate before and after transplantation were considerably lower than the control group; a significant effect of tacrolimus has not been observed (7.32 ⫾ 4.68 ng/mL and 7.55 ⫾ 5.20 ng/mL). Serum vitamin B12 levels in the transplant group were significantly lower than the control group; a significant decline was seen 3 months after the renal transplantation (448.94 ⫾ 230.03 pg/mL vs 334.38 ⫾ 240.61 pg/mL). Consequently, although plasma homocysteine levels of renal transplant recipients are higher, a lowering effect of tacrolimus therapy was not observed on plasma homocysteine levels. The lower levels of folate and Vitamin B12 in the transplant group compared to a control group supports therapy with folate and Vitamin B12 to decrease homocysteine concentrations.
H
YPERHOMOCYSTEINEMIA represents an independent risk factor for the development of atherosclerotic cardiovascular disease among patients with normal and impaired renal function.1 Although, renal transplantation reduces plasma homocysteine levels, they still remain high compared to healthy subjects.2 Homocysteine is a thiol-containing amino acid produced by the intracellular demethylation of methionine. Homocysteine is metabolized by either cysteine or methionine. In the vitamin B6 dependent trans-sulfhuration pathway, homocysteine is metabolized to cysteine. A major portion of the homocysteine is remethylated to methionine, mainly by the folate and cobalamin-dependent enzyme methionine synthase. When these reactions are impaired due to deficiencies of folate and cobalamin or renal failure, homocysteine accumulates and is excreted into the blood.3 A majority of scientific literature suggest that the normal value between 5 and 15 © 2004 by Elsevier Inc. All rights reserved. 360 Park Avenue South, New York, NY 10010-1710 Transplantation Proceedings, 36, 159⫺160 (2004)
mol/L. 5 mol/L increase in total homocysteine level is associated with the risk of cardiovascular disease.4 Studies of renal transplant patients indicate that increased homocysteine levels are associated with the risk of cardiovascular disease. However the factors contributing to the hyperhomocysteinemia have not clearly been determined in these patients. Among these factors are the reduced renal function and low serum folate. The association between cyclosporine treatment and increased homoFrom Akdeniz University, Faculty of Medicine, Departments of Central Laboratory (S.H.A., M.G.), Nephrology (M.T., A.Y., F.E.), General Surgery (A.G., A.D., M.A.), and Transplant Center (L.Y.), Antalya Turkey. Address reprint requests to S. Halide Akbas¸, Akdeniz University, Faculty of Medicine, Central Laboratory, Clinical Biochemistry Unit, Antalya, Turkey. E-mail: [email protected] 0041-1345/04/$–see front matter doi:10.1016/j.transproceed.2003.11.059 159
AKBAS¸ , TUNCER, GU¨ RKAN ET AL
160 Table 1. Plasma Homocysteine, Serum Folate, and Vitamin B12 Levels Control
Baseline
3 Months
Homocysteine 8.21 ⫾ 1.72* 16.84 ⫾ 6.43 16.02 ⫾ 6.54 (mol/L) Folate (ng/mL) 11.55 ⫾ 3.18* 7.32 ⫾ 4.68 7.55 ⫾ 5.20 Vitamin B12 547.30 ⫾ 166.57* 448.94 ⫾ 230.03 334.38 ⫾ 240.61** (pg/mL) Values are expressed as mean ⫾ SD. *P ⬍ .05 for comparison with renal transplant group. **P ⬍ .05 for comparison with baseline (before transplantation) value.
cysteine levels in renal transplanted patients was documented.5– 6 However, there is conflicting data on the influence of tacrolimus on the plasma homocysteine level.2–7 Therefore, we evaluated plasma homocysteine levels and factors known to influence homocysteine metabolism (folate and vitamin B12) in cadaveric renal transplant patients treated with tacrolimus in this study. MATERIALS AND METHODS Plasma homocysteine, serum folate and vitamin B12 levels were measured in blood samples of 18 cadaveric renal transplant patients (12 men; 6 women, mean age is 35 ⫾ 10.43 years) before and 3 months after transplantation. 20 control subjects who were matched by age and gender with the patients underwent measurement of the same analytes in their blood samples. No patient received treatment with folate or vitamin B12. Blood samples were drawn after an overnight fast. Plasma homocysteine concentrations were measured using a Fluorescence Polarization Immunoassay (FPIA) on the IMx analyser (Abbott Laboratories, Abbott Park, IL, USA). Serum folate and vitamin B12 concentrations were measured by a competitive immunoassay on the Immulite 2000 analyzer (DPC, CA, USA). Results are expressed as mean values ⫾ SD. The Student “t” test was used to compare differences between groups. The Pearson test was employed to evaluate correlations between variables. P ⬍ .05 was considered statistically significant.
RESULTS
Among control subjects, the mean plasma homocysteine concentration was 8.21 ⫾ 1.72 mol/L; mean serum Vitamin B12 concentration, 547.3 ⫾ 166.57 pg/mL; and mean serum folate concentration, 11.55 ⫾ 3.18 ng/mL. As shown in Table 1, the mean plasma homocysteine levels before and after transplantation were significantly higher among the control group; no significant change was observed at the end of third month among patients treated with tacrolimus (16.84 ⫾ 6.43 mol/L vs 16.02 ⫾ 6.54 mol/L). There was no relationship between tacrolimus level and plasma homocysteine concentration. The levels of folate before and after transplantation were considerably lower than the control group. No significant effect of transplantation under tacrolimus therapy with folate levels was observed during the 3 month period (7.32 ⫾ 4.68 ng/mL vs 7.55 ⫾ 5.20 ng/mL). On the contrary, a significant negative correlation was found between serum
folate and plasma homocysteine values in the transplant group (r ⫽ ⫺.365, P ⬍ .05). While the serum vitamin B12 level prior to the transplantation was 448.94 ⫾ 230.03 pg/mL, at the end of the third month following the procedure was considerably lower, 334.38 ⫾ 240.61 pg/mL. In addition, the levels of serum vitamin B12 decreased significantly compared to the control group (Table 1). DISCUSSION
Cardiovascular disease is the most common cause of death among renal transplant recipients. Plasma homocysteine concentrations are significantly higher among renal transplant patients.8 In our study, we observed higher homocysteine levels in renal transplant recipients compared to the control group. Tacrolimus therapy had no effect on homocysteine levels. Ignatescu et al. reported that while tacrolimus exerted no effect on homocysteine levels, a finding similar to our results, whereas MMF therapy produced a significant decrease in homocysteine levels in renal transplant patients.9 In a much larger study of 50 renal transplants, Stein et al. was unable to find a correlation between total homocysteine concentration or its metabolites with immunosuppressive treatment (cyclosporine vs tacrolimus).1 However, prospective studies are required to confirm these results. In our study the lower levels of folate and Vitamin B12 in the transplant group compared with the control group suggests the potential benefit of folate and Vitamin B12 supplement therapy to decrease homocysteine concentrations, reduce cardiovascular risk, and improve long-term outcomes. REFERENCES 1. Stein G, Muller A, Busch M, et al: Homocysteine, its metabolites, and B group vitamins in renal transplant patients. Kidney Int 59(Suppl 78):262, 2001 2. Quirogo I, Morris-Stiff G, Baboo R, et al: Differential homocysteine levels in renal transplant patients receiving neoral versus tacrolimus. Transplant Proc 33:1209, 2001 3. Ueland PM: Homocysteine species as components of plasma redox thiol status. Clin Chem 41:340, 1995 4. Boushey CJ, Beresford SAA, Omenn GS, et al: A quantitative assessment of plasma homocysteine as a risk factor for vascular disease. JAMA 274:1049, 1995 5. Arnadottir M, Hultberg B, Vladov V, et al: Hyperhomocysteinemia in cyclosporin treated renal transplant recipients. Transplantation 65:544, 1998 6. Cole DE, Ross HJ, Evrovski J, et al: Correlation between total homocysteine and cyclosporine concentrations in cardiac transplant recipients. Clin Chem 44:2307, 1998 7. Artz MA, Boots JMM, Ligtenberg G: Randomized conversion from cyclosporine to tacrolimus in renal transplant patients: improved lipid profile and unchanged plasma homocysteine levels. Transplant Proc 34:1793, 2002 8. Ducloux D, Ruedin C, Gibey R, et al: Prevalance, determinants and clinical significance of hyperhomocysteinemia in renal transplant recipients. Nephrol Dial Transplant 13:2890, 1998 9. Ignatescu MC, Kletzmayr J, Fodinger M, et al: Influence of mycophenolic acid and tacrolimus on homocysteine metabolism. Kidney Int 61:1894, 2002
H
YPERHOMOCYSTEINEMIA represents an independent risk factor for the development of atherosclerotic cardiovascular disease among patients with normal and impaired renal function.1 Although, renal transplantation reduces plasma homocysteine levels, they still remain high compared to healthy subjects.2 Homocysteine is a thiol-containing amino acid produced by the intracellular demethylation of methionine. Homocysteine is metabolized by either cysteine or methionine. In the vitamin B6 dependent trans-sulfhuration pathway, homocysteine is metabolized to cysteine. A major portion of the homocysteine is remethylated to methionine, mainly by the folate and cobalamin-dependent enzyme methionine synthase. When these reactions are impaired due to deficiencies of folate and cobalamin or renal failure, homocysteine accumulates and is excreted into the blood.3 A majority of scientific literature suggest that the normal value between 5 and 15 © 2004 by Elsevier Inc. All rights reserved. 360 Park Avenue South, New York, NY 10010-1710 Transplantation Proceedings, 36, 159⫺160 (2004)
mol/L. 5 mol/L increase in total homocysteine level is associated with the risk of cardiovascular disease.4 Studies of renal transplant patients indicate that increased homocysteine levels are associated with the risk of cardiovascular disease. However the factors contributing to the hyperhomocysteinemia have not clearly been determined in these patients. Among these factors are the reduced renal function and low serum folate. The association between cyclosporine treatment and increased homoFrom Akdeniz University, Faculty of Medicine, Departments of Central Laboratory (S.H.A., M.G.), Nephrology (M.T., A.Y., F.E.), General Surgery (A.G., A.D., M.A.), and Transplant Center (L.Y.), Antalya Turkey. Address reprint requests to S. Halide Akbas¸, Akdeniz University, Faculty of Medicine, Central Laboratory, Clinical Biochemistry Unit, Antalya, Turkey. E-mail: [email protected] 0041-1345/04/$–see front matter doi:10.1016/j.transproceed.2003.11.059 159
AKBAS¸ , TUNCER, GU¨ RKAN ET AL
160 Table 1. Plasma Homocysteine, Serum Folate, and Vitamin B12 Levels Control
Baseline
3 Months
Homocysteine 8.21 ⫾ 1.72* 16.84 ⫾ 6.43 16.02 ⫾ 6.54 (mol/L) Folate (ng/mL) 11.55 ⫾ 3.18* 7.32 ⫾ 4.68 7.55 ⫾ 5.20 Vitamin B12 547.30 ⫾ 166.57* 448.94 ⫾ 230.03 334.38 ⫾ 240.61** (pg/mL) Values are expressed as mean ⫾ SD. *P ⬍ .05 for comparison with renal transplant group. **P ⬍ .05 for comparison with baseline (before transplantation) value.
cysteine levels in renal transplanted patients was documented.5– 6 However, there is conflicting data on the influence of tacrolimus on the plasma homocysteine level.2–7 Therefore, we evaluated plasma homocysteine levels and factors known to influence homocysteine metabolism (folate and vitamin B12) in cadaveric renal transplant patients treated with tacrolimus in this study. MATERIALS AND METHODS Plasma homocysteine, serum folate and vitamin B12 levels were measured in blood samples of 18 cadaveric renal transplant patients (12 men; 6 women, mean age is 35 ⫾ 10.43 years) before and 3 months after transplantation. 20 control subjects who were matched by age and gender with the patients underwent measurement of the same analytes in their blood samples. No patient received treatment with folate or vitamin B12. Blood samples were drawn after an overnight fast. Plasma homocysteine concentrations were measured using a Fluorescence Polarization Immunoassay (FPIA) on the IMx analyser (Abbott Laboratories, Abbott Park, IL, USA). Serum folate and vitamin B12 concentrations were measured by a competitive immunoassay on the Immulite 2000 analyzer (DPC, CA, USA). Results are expressed as mean values ⫾ SD. The Student “t” test was used to compare differences between groups. The Pearson test was employed to evaluate correlations between variables. P ⬍ .05 was considered statistically significant.
RESULTS
Among control subjects, the mean plasma homocysteine concentration was 8.21 ⫾ 1.72 mol/L; mean serum Vitamin B12 concentration, 547.3 ⫾ 166.57 pg/mL; and mean serum folate concentration, 11.55 ⫾ 3.18 ng/mL. As shown in Table 1, the mean plasma homocysteine levels before and after transplantation were significantly higher among the control group; no significant change was observed at the end of third month among patients treated with tacrolimus (16.84 ⫾ 6.43 mol/L vs 16.02 ⫾ 6.54 mol/L). There was no relationship between tacrolimus level and plasma homocysteine concentration. The levels of folate before and after transplantation were considerably lower than the control group. No significant effect of transplantation under tacrolimus therapy with folate levels was observed during the 3 month period (7.32 ⫾ 4.68 ng/mL vs 7.55 ⫾ 5.20 ng/mL). On the contrary, a significant negative correlation was found between serum
folate and plasma homocysteine values in the transplant group (r ⫽ ⫺.365, P ⬍ .05). While the serum vitamin B12 level prior to the transplantation was 448.94 ⫾ 230.03 pg/mL, at the end of the third month following the procedure was considerably lower, 334.38 ⫾ 240.61 pg/mL. In addition, the levels of serum vitamin B12 decreased significantly compared to the control group (Table 1). DISCUSSION
Cardiovascular disease is the most common cause of death among renal transplant recipients. Plasma homocysteine concentrations are significantly higher among renal transplant patients.8 In our study, we observed higher homocysteine levels in renal transplant recipients compared to the control group. Tacrolimus therapy had no effect on homocysteine levels. Ignatescu et al. reported that while tacrolimus exerted no effect on homocysteine levels, a finding similar to our results, whereas MMF therapy produced a significant decrease in homocysteine levels in renal transplant patients.9 In a much larger study of 50 renal transplants, Stein et al. was unable to find a correlation between total homocysteine concentration or its metabolites with immunosuppressive treatment (cyclosporine vs tacrolimus).1 However, prospective studies are required to confirm these results. In our study the lower levels of folate and Vitamin B12 in the transplant group compared with the control group suggests the potential benefit of folate and Vitamin B12 supplement therapy to decrease homocysteine concentrations, reduce cardiovascular risk, and improve long-term outcomes. REFERENCES 1. Stein G, Muller A, Busch M, et al: Homocysteine, its metabolites, and B group vitamins in renal transplant patients. Kidney Int 59(Suppl 78):262, 2001 2. Quirogo I, Morris-Stiff G, Baboo R, et al: Differential homocysteine levels in renal transplant patients receiving neoral versus tacrolimus. Transplant Proc 33:1209, 2001 3. Ueland PM: Homocysteine species as components of plasma redox thiol status. Clin Chem 41:340, 1995 4. Boushey CJ, Beresford SAA, Omenn GS, et al: A quantitative assessment of plasma homocysteine as a risk factor for vascular disease. JAMA 274:1049, 1995 5. Arnadottir M, Hultberg B, Vladov V, et al: Hyperhomocysteinemia in cyclosporin treated renal transplant recipients. Transplantation 65:544, 1998 6. Cole DE, Ross HJ, Evrovski J, et al: Correlation between total homocysteine and cyclosporine concentrations in cardiac transplant recipients. Clin Chem 44:2307, 1998 7. Artz MA, Boots JMM, Ligtenberg G: Randomized conversion from cyclosporine to tacrolimus in renal transplant patients: improved lipid profile and unchanged plasma homocysteine levels. Transplant Proc 34:1793, 2002 8. Ducloux D, Ruedin C, Gibey R, et al: Prevalance, determinants and clinical significance of hyperhomocysteinemia in renal transplant recipients. Nephrol Dial Transplant 13:2890, 1998 9. Ignatescu MC, Kletzmayr J, Fodinger M, et al: Influence of mycophenolic acid and tacrolimus on homocysteine metabolism. Kidney Int 61:1894, 2002