Role of Folic Acid in Atherosclerosis After Kidney Transplant: A Double-blind, Randomized, Placebo-controlled Clinical Trial
Objectives: We investigated the effects of folic acid supplementation on plasma total homocysteine levels and carotid intima-media thickness after kidney transplant.
Materials and Methods: Sixty patients who had undergone a kidney transplant were studied in this double-blind, randomized, placebo-controlled clinical trial. Those subjects were randomized to receive either 5 mg/d of oral folic acid or an equivalent dosage of placebo. The main outcome variables were the plasma total homocysteine level and carotid intima-media thickness (determined via B-mode sonography) at baseline and 2, 4, and 6 months after kidney transplant. We used independent and paired sample t tests for data analysis.
Results: The mean age of the patients was 40.9 ± 10 years, and 32 of those subjects (58.2%) were men. In the control group, the plasma total homocysteine levels were 19 µmol/L at baseline, 18.7 µmol/L after 2 months, 19.3 µmol/L after 4 months, and 20 µmol/L after 6 months; and the carotid intima-media thickness measurements were 0.81 mm at baseline, 0.82 mm after 2 months, 0.84 mm after 4 months, and 0.85 mm after 6 months. In the folic acid group, the plasma total homocysteine levels were 18.5 µmol/L at baseline, 4.7 µmol/L after 2 months, 12.9 µmol/L after 4 months, and 10.9 µmol/L after 6 months; and the carotid intima-media thickness measurements were 0.73 mm at baseline, 0.73 mm after 2 months, 0.72 mm after 4 months, and 0.71 mm after 6 months.
Conclusions: Folic acid supplementation reduces both the plasma total homocysteine level and carotid intima-media thickness shortly after kidney transplant.
Key words: Kidney transplant, Atherosclerosis, Homocysteine, Folic acid, Carotid intima-media thickness, Doppler, Ultrasonography
Atherosclerosis and its consequences are the leading causes of morbidity and mortality after kidney transplant, and such problems decrease the overall success of kidney transplant with respect to the patient’s longevity (1-3). However, a kidney transplant reduces the incidence of some cardiovascular morbidities such as left ventricular hypertrophy and volume overload (4). Prior studies have shown that, primarily because of various risk factors, a successful renal transplant may not completely normalize the risk of cardiovascular events or morphologic changes in vessel structure (5,6). One of the important risk factors that contributes to the development and progression of cardiovascular problems in kidney transplant recipients is homocysteine (Hcy) (7-9).
Homocysteine is an intermediate product of methionine metabolism. An elevated level of Hcy has a negative effect on endothelial cells, coagulation factors, and platelet function (10-12) and could lead to adverse structural changes in carotid artery properties (13) that can be detected in several ways. One of the most frequently used and reliable markers for such changes is the carotid intima-media thickness as determined by B-mode Doppler sonography (14). Carotid intima-media thickness, which is useful in predicting cardiovascular outcome in several patient populations (14-16), appears to be a feasible, reliable, valid, and cost-effective method for use in population studies and clinical trials of atherosclerosis progression and regression (10).
Prior studies have shown that a successful reduction in the plasma total homocysteine (tHcy) level can lead to a decrease in carotid intima-media thickness and the incidence of cardiovascular events (3, 4, 17, 18). Some studies have shown that after kidney transplant, the level of tHcy will increase gradually but never reaches a level within normal limits (1). It thus seems that the treatment of hyperhomocysteinemia after kidney transplant is beneficial (19). Supplementation with B vitamins and folic acid is the treatment of choice for hyperhomocysteinemia (20, 21) and could lead to a reduction in cardiovascular risk and carotid intima-media thickness in the general population (11, 12, 21). However, there is not enough evidence to support the effectiveness of folic acid in treating hyperhomocysteinemia or decreasing the carotid intima-media thickness after kidney transplant. We designed a double-blind, randomized, placebo-controlled clinical trial to investigate that issue in kidney transplant recipients.
Materials and Methods
Except for the total cholesterol level, all other measured variables did not differ between the treated and control groups. Supplementation with folic acid caused a significant increase in the plasma folic acid level in the treated group (from 5.4 ± 3.1 mmol/L at baseline to 7.9 ± 4.4 mmol/L, 8.9 ± 4.4, mmol/L and 10.2 ± 4.5 mmol/L at 2, 4, and 6 months, respectively; P value for each interval compared with baseline, < .05). There was no significant change in the plasma level of folic acid in the control group.
During the first 2 months of study, the level of tHcy decreased significantly in the folic acid group (from 18.5 ± 7 µmol/L to 14.7 ± 3.8 µmol/L, P < .001). Such a significant decrease did not occur in the control group (Figure 2). The tHcy level in the folic acid group was significantly lower than that in the control (P = .006). At 2 months, the carotid intima-media thickness was slightly higher than the baseline level in the control group, but that increase was not statistically significant. The carotid intima-media thickness in the folic acid group did not change significantly from the baseline level. The increase in the carotid intima-media thickness in the control group at 2 months made the difference of carotid intima-media thickness between folic acid and control group to a significant level (P = .044) (Figure 3).
After 4 months of study, the level of tHcy continued to decrease in the folic acid group and reached 12.9 ± 2.6 µmol/L, which was significantly lower than the baseline value (P < .001). The level of tHcy, which reached 19.3 ± 6.8 µmol/L in the control group, had not changed significantly from the baseline value at that time. Again, the level of tHcy in the folic acid group was significantly lower than that in the control group (P = .007). The carotid intima-media thickness in the folic acid group decreased to 0.72 ± 0.1 mm, which was significantly lower than the baseline thickness (P = .042). The carotid intima-media thickness had increased significantly from the baseline thickness in the control group and reached 0.84 ± 0.2 mm (P = .024). There was also a significant difference between the carotid intima-media thickness in the folic acid and that in the control group (P =.007)
At the end of the study (ie, 6 months after the study initiation), the tHcy values and carotid intima-media thickness in the folic acid group were significantly lower than baseline (10.9 ± 2.1, 0.71 ± 0.1 µmol/L; P < .001 and P = .011, respectively). In the control group, the tHcy level reached 20 ± 6.9 µmol/L, which was not significantly higher than baseline (P = .342). The carotid intima-media thickness in the control group reached 0.85 ± 0.2 mm, which was significantly higher than baseline (P = .003). When we compared the 2 groups, we found that tHcy values and carotid intima-media thickness were both significantly lower in the folic acid group than in the control group (P <.001 and P = .003; respectively). During the study, the lipid profile (ie, the levels of total cholesterol, high-density lipoprotein, low-density lipoprotein, and triglycerides) was not significantly different nor from the baseline measure in each group, neither between the folic acid and control group (Figure 4).
In our study, we observed that folic acid, when administered in a dosage of 5 mg/d to patients who had undergone a kidney transplant, reduced both the tHcy level to a significant degree (which was detected after 2 months of therapy) and the carotid intima-media thickness. That decrease continued throughout the study. The carotid intima-media thickness also decreased in the folic acid group during the study, and that decrease was significant after 4 months of folic acid treatment. In the control group, however, the total homocysteine level and carotid intima-media thickness increased during the study. The increase in the carotid intima-media thickness was significant 4 months after the kidney transplant.
Although the level of tHcy might be expected to decrease after a kidney transplant, a study by Suwelack and colleagues showed no significant decrease in that level during the first 12 months of follow-up after kidney transplant in a subgroup of patients with baseline tHcy values similar to those in our patients (13). In another study of patients who underwent a kidney transplant and were monitored for up to 252 months, Sobki and colleagues found that there was a significant correlation between the tHcy level and the posttransplant interval (22). This suggests that the tHcy level increases gradually after a kidney transplant; thus patients with a transplanted kidney might be expected to have higher a tHcy level than that in the healthy population. This finding was found in similar studies, such as that performed by Marcucci and colleagues, who found that hyperhomocysteinemia is highly prevalent after kidney transplant (23). We found similar results, and in our study, a gradual and nonsignificant increase in the level of tHcy occurred in the control group.
In a study on change in the carotid intima-media thickness after a kidney transplant, De Lima and colleagues found that 12 months after surgery, the carotid morphological parameters had increased above baseline, but that increase was not significant (5). Forty months after a successful kidney transplant, the carotid intima-media thickness in their subjects had significantly decreased (5). In another study, there was no improvement in the carotid intima-media thickness of the patients 1 year after a kidney transplant (24). In other research, Jogestrand and colleagues (25) and Suwelack and colleagues (26) compared carotid artery characteristics in patients who had undergone a kidney transplant with those in healthy individuals. Those authors found that a short time after kidney transplant, the levels of carotid atherosclerosis markers were significantly increased. In our study, 4 months after a kidney transplant, the carotid intima-media thickness in the control group was significantly higher than baseline. That increase was also observed in the sixth month of the study.
Our results are similar to those of previous studies (23, 27, 28) showing that supplementation with folic acid lowers elevated levels of tHcy in the short term and over time. We found, as have other authors who reported on the role of folic acid supplementation in reducing carotid intima-media thickness and the incidence of cardiovascular accidents (28-30), that folic acid therapy is similarly useful after a kidney transplant. In their study of 10 kidney transplant recipients, Austen and colleagues found that after 3 months of therapy with folic acid and despite a significant decrease in the tHcy level, there was no significant change in the brachial artery intima-media thickness of their subjects (31). Ours findings were similar. We observed no change in the subjects’ carotid intima-media thickness during the first 4 months of the study, and it was only later that we noted a reduction in the carotid intima-media thickness in the folic acid group. It seems that folic acid therapy must be administered for several months before its beneficial effects occur. The changes in carotid intima-media thickness seemed not to be the effect of other factors such as age, the duration of chronic renal failure, or hemodialysis therapy because there was no significant difference associated with those factors in our 2 study groups. Our subjects had no history of cardiovascular disease, diabetes mellitus, or cigarette smoking, all of which could affect the carotid intima-media thickness of the participants. We also observed no significant difference or change in the lipid profile of our subjects before and during the study. We can thus with more confidence attribute the changes in carotid intima-media thickness to the alterations that occurred in the subjects’ tHcy levels as a result of folic acid treatment.
Because of the high prevalence of cardiovascular events that occur during early posttransplant months (32), we agree that aggressive intervention is needed during the first year after a kidney transplant to prevent the development of a cardiovascular event (33). We believe that the beneficial effects of a kidney transplant on atherosclerotic indices do not occur for several months after surgery and that during that interval, patients have a relatively greater risk of experiencing a cardiovascular event. Because of the adverse sequelae of having undergone a kidney transplant (eg, recurrent hospitalizations or infections and the effects of immunosuppressive therapy), it seems wise not to impose a greater risk of cardiovascular accidents on such patients, especially when those events could be prevented by using a simple treatment like administration of folic acid. Other interventions (eg, steroid-free immunosuppressive therapy  or a reduction in the cyclosporine dose ), which are useful in reducing the plasma tHcy level and the risk of cardiovascular disease, should also be considered when possible.
Our study has some limitations. The relatively small sample size is a major limitation in generalizing the results. Also, the brief follow-up limited our ability to determine the long-term effects of our intervention on the patient population studied. The power of our study lies in our use of valid measures and methods to evaluate atherosclerotic status and to determine the subjects’ plasma level of tHcy.
In summary, we found that administering supplementary folic acid 5 mg/d after kidney transplant led to a reduction in the subjects’ plasma tHcy level and reduced carotid intima-media thickness. Those findings were detectable shortly after treatment with supplementary folic acid was initiated.
Volume : 7
Table 1. Study inclusion and exclusion criteria
Figure 1. Enrollment and randomization of the study subjects
Table 2. Demographic and baseline variables of the study groups
Figure 2. Total homocysteine levels in the study subjects
Figure 3. Changes in intima-media thickness after kidney transplant in the
Figure 4. Changes in the lipid profile of the study subjects
Copyright © Baskent University 2003. Printed in Turkey. All Rights Reserved.