Hyperhomocysteinemia and transplant coronary artery disease in cardiac transplant recipients

Long-term effect of folic acid therapy in heart transplant recipients: follow-up analysis of a randomized study

BACKGROUND

Folic acid therapy reduces homocysteine plasma levels, which seem to influence occurrence of cardiac allograft vasculopathy, but its effect on medium- or long-term prognosis after heart transplantation is unknown.

METHODS

We analyzed 7-year outcome of 51 recipients randomized to receive 15 mg/day of methyltertrahydrofolate for 1 year after heart transplantation or standard therapy alone (originally, for intravascular ultrasound study of short-term cardiac allograft vasculopathy progression); recipients were observed for a further 5 to 6 years.

RESULTS

Overall, 13 deaths occurred (six oncologic, five cardiovascular, two infective). Estimated 7-year survival was better in recipients randomized to folate (88%+/-6% vs. 61%+/-9%, P=0.04). After adjusting for age, pretransplant coronary artery disease, and hyperhomocysteinemia, posttransplant folic acid therapy was associated with lower mortality (relative risk [RR] 0.53, 95% confidence interval [CI] 0.25-0.97; P=0.036), apparently driven by reductions in both cancer-related and cardiovascular causes. Reduced mortality was marked in a high-risk subgroup comprising older recipients and patients transplanted because of coronary artery disease (RR 0.43, 95% CI 0.17-0.85) but not in the lower-risk subgroup (RR 1.11, 95% CI 0.22-5.61).

CONCLUSIONS

Although further studies are needed, it seems reasonable to suggest folate therapy to heart transplant recipients. It is possible that properties other than homocysteine reduction may provide antitumoral benefits.

Cardiac Allograft Vasculopathy: An Update

Allograft vasculopathy remains the nemesis of long-term survival in heart transplantation. Possible modifying risk factors such as obesity, diabetes, and hypertension should continue to be pursued aggressively. All patients should receive statins. Clinical trials will provide the evidence needed to ascertain whether mammalian target of rapamycin inhibitors should be used in de novo cardiac transplant recipients to attenuate cardiac allograft vasculopathy (CAV). Intravascular ultrasound appears to play a key role in the diagnosis and evaluation of new treatments, and may indeed represent a surrogate marker that can be used to tailor management and improve outcomes. A better understanding of CAV is needed to develop targeted preventive therapies. Ongoing research in native atherosclerosis and vascular biology may provide answers within the next decade.

Thromboembolism in Heart Transplantation: Role of Prothrombin G20210A and Factor V Leiden

BACKGROUND

Thromboembolism has been reported as a frequent complication after cardiac transplantation. Many risk factors for thrombosis may explain this, such as metabolic alterations and the use of cyclosporine. In the general population, two single nucleotide polymorphisms (SNPs), factor V Leiden and prothrombin G20210A (PT G20210A), have been associated with a significant increase in the risk of thrombosis. However, these mutations have not been analyzed in cardiac transplant patients. We describe the protracted history of recurrent thromboembolism in a rare case of homozygosity for the PT G20210A variant. This prompted us to analyze the entire cardiac transplant cohort for the incidence of thromboembolic events and their association with these genetic polymorphisms.

METHODS

We report the study of 84 cardiac transplant recipients. We retrospectively analyzed the frequency of thromboembolic episodes. The genotypes for FVL and PT G20210A were determined and correlated with those episodes.

RESULTS

Our results confirm a very high incidence of thromboembolism in this population. We also found a significant increase in the likelihood of thromboembolism in subjects with the PTB G20210A variant (odds ratio 3.08; 95% confidence interval: 1.7-5.5).

CONCLUSIONS

The incidence of thromboembolic complications after heart transplantation is increased and may be related in part to genetic predisposition.

Genetic polymorphisms predisposing to hyperhomocysteinemia in cardiac transplant patients

Genetic determinants for high homocysteine (Hcy) levels are now well known. We studied several single nucleotide polymorphisms (SNP) in Hcy-regulating genes [methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C; methionine synthase (MS) A2756G; methionine synthase reductase (MTRR) A66G] in relation to total plasma Hcy levels, transplant coronary artery disease and thromboembolic episodes in 84 heart transplant patients, and we compared the incidence of these polymorphisms with those in a healthy adult controls. At least one copy of the G allele of the MTRR A66G SNP was found in a significantly greater proportion of cardiac transplant (CTX) recipients compared with controls (94.0% vs. 79.9% respectively). None of the SNP analyzed were correlated with total Hcy plasma levels or the presence of transplant coronary artery disease. However, MS A2756G was significantly associated with cobalamin levels (AA genotype: 290 +/- 122 pmol/l; AG: 381 +/- 151 pmol/l and GG: 415 +/- 100 pmol/l), as was MTRR A66G (AA: 478 +/- 219 pmol/l, AG: 306 +/- 124 pmol/l and GG: 306 +/- 123 pmol/l). MTRR A66G was also correlated with serum folate. No association was found with thromboembolic events. In conclusion, there was a significant difference in the frequency of the G allele genotype of the MTRR A66G in CTX patients versus controls. Differences in cobalamin and folate levels with the MTRR A66G and MS A2756G polymorphisms were noted. Thus, SNP in Hcy-regulating genes may be important determinants of vitamin metabolism in CTX, raising the question of increased vitamin requirements to minimize increased plasma Hcy in this high-risk group.

Blood glutathione as a marker of cardiac allograft vasculopathy in heart transplant recipients

BACKGROUND

Cardiac allograft vasculopathy (CAV) limits survival after heart transplantation (HTx). Between immunologic and non-immunologic factors, reactive oxygen species generation has been proposed as pathogenetic mechanism. This study was aimed at evaluating redox status in HTx recipients and verifying whether it could be independently associated with CAV.

METHODS

Fifty-five consecutive male HTx recipients, median [interquartile range] age 60 yr [50, 64], underwent angiography 67 months [21, 97] after HTx to assess CAV, defined as significant stenosis in >or=1 epicardial vessel or any distal vessel attenuation. All patients underwent blood sampling 89 months [67, 119] after HTx for biochemical (glucose, creatinine, total and LDL cholesterol, and cyclosporin levels) and redox evaluation [plasma reduced and total homocysteine, cysteine, cysteinylglycine, glutathione, blood reduced glutathione (GSH(bl)) and vitamin E]. Univariate Odds Ratios (OR) with 95% confidence interval (95% CI, highest vs. lowest quartile) were estimated on the basis of a logistic regression analysis between clinical, conventional biochemical and redox data. Only the significant variables at univariate entered into multivariate analysis.

RESULTS

CAV was documented in 15 (27%) patients. Univariate analysis showed that time from HTx to angiography (OR 3.97, 95% CI 1.15-14, p = 0.03) and GSH(bl) (OR 0.31, 95% CI: 0.14-0.70, p = 0.005) were significantly associated with CAV. However, multivariate analysis revealed GSH(bl) as the only independent predictor of CAV (OR 0.31, 95% CI: 0.13-0.74, p = 0.008).

CONCLUSIONS

In HTx recipients reduced levels of GSH(bl) are independently associated with CAV. Given its potent intracellular scavenger properties, GSH(bl) may serve as a marker of antioxidant defence consumption, favouring CAV development.

Effects of folic acid fortification and multivitamin therapy on homocysteine and vitamin b12 status in cardiac transplant recipients

BACKGROUND

Hyperhomocysteinemia is a frequent finding after cardiac transplantation, but increased folate intake induces a decrease in total homocysteine concentrations. In 1998, food in Canada was fortified nationwide with folic acid. We assessed the impact of routine folate fortification on homocysteine concentrations in our cardiac transplant population.

METHODS

In 18 subjects, we measured total homocysteine (tHcy), serum folate, and cobalamin concentrations in 1997 (before folate fortification) and in 1998 (after fortification). We repeated the analysis after specific multivitamin supplementation for 10 weeks.

RESULTS

We found a significant decrease in baseline tHcy concentrations and in folate concentrations between 1997 and 1998. However, we also found a decrease in serum cobalamin concentrations. We found a correlation between decreased cobalamin concentrations and the methionine synthase A2756G genotype, but not with other common polymorphisms associated with homocysteine metabolism. After multivitamin supplementation, we observed a trend toward further decrease in tHcy concentrations and a significant increase in serum folate and cobalamin concentrations. Finally, we measured serum methylmalonic acid concentrations, an index of tissue cobalamin status. We did not find a correlation between increased methylmalonic acid concentrations and decreased serum cobalamin, perhaps related to the confounding effect of altered renal status on methylmalonic acid excretion.

CONCLUSIONS

National folate fortification was associated with decreased tHcy and increased folate concentrations in our cardiac transplant population. Additional administration of vitamin supplements induced a further decrease in tHcy and an increase in folate. Finally, folate fortification unveiled cobalamin deficiency in some patients, associated with the methionine synthase A2756G mutation.

Coronary artery vasculopathy in pediatric cardiac transplant patients: the therapeutic potential of immunomodulators

The single largest cause of late graft loss in pediatric cardiac transplantation is transplant coronary artery vasculopathy (CAV). The mechanism of CAV remains unknown; it appears to have both immune and non-immune causes. The final common pathway of these mechanisms is endothelial activation, a prothrombotic environment, and endothelial damage with subsequent diffuse intimal proliferation. The disease process has largely been thought to be progressive and unresponsive to treatment. Re-transplantation has been advocated as the only definitive treatment. The appropriate management is largely unknown; intervention or surgical management has had limited utility, while medical management appears to have the most promise. Improvement in outcome can be achieved by optimizing non-immune factors and aggressive management of the immune mechanisms. Long-term survival of transplant patients after diagnosis with CAV is now being reported.