Homocysteine--a treatable risk factor for allograft vascular disease after heart transplantation?

Pyridoxal-5'-phosphate deficiency after intestinal and multivisceral transplantation

BACKGROUND

Successful intestinal transplantation is measured by the achievement of clinical nutritional autonomy (CNA). However, the ability of the graft to maintain normal micronutrient levels including vitamins has yet to be thoroughly evaluated.

OBJECTIVE

After an initial clinical observation of isolated cases of pyridoxal-5'-phosphate (PLP) deficiency, this prospective study was designed to address the incidence of, risk factors for, and management of PLP deficiency in adult intestinal transplant recipients.

DESIGN

Serum PLP and homocysteine concentrations were prospectively measured before and after transplantation at frequent intervals.

RESULTS

PLP deficiency occurred in 10% of candidates and in 96% of recipients within a median onset of 30 d (range: 4-118 d) after transplantation. Of this group, 41% were receiving parenteral nutrition (PN), 41% were receiving enteral feeding, and the remaining 18% had already achieved CNA. The overall cumulative risk was 24% at 15 d, 59% at 30 d, 79% at 45 d, and 90% at 90 d; none of the risk factors, including homocysteine concentrations, were significant. Nonetheless, the development of PLP deficiency during PN therapy was associated with a significant (P < 0.001) delay in the achievement of CNA. Despite development of severe deficiency in most cases, none of the subjects experienced clinical manifestations of PLP deficiency because of prompt replacement therapy.

CONCLUSIONS

Serial monitoring of serum PLP concentrations is recommended for PN-dependent patients with short-bowel syndrome before and after transplantation for early detection and prompt initiation of preemptive therapy. Long-term measurement at frequent intervals is also recommended, particularly for transplant recipients, to diagnose late deficiency despite achievement of CNA and to prevent toxicity from overdose.

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.

Treatment of allograft vasculopathy in heart transplantation

Cardiac allograft vasculopathy remains one of the main causes of morbidity and mortality after heart transplantation, although its impact is becoming somewhat smaller as prophylactic measures are implemented. Advances in the understanding of the molecular and cellular mechanisms involved in the genesis and development of cardiac allograft vasculopathy are opening ways for new diagnostic and therapeutic strategies. Successful prophylaxis of the early stages of the disease has been demonstrated with the use of newer immunosuppressive agents, such as sirolimus and everolimus, that will probably be included in future protocols. For most patients with established cardiac allograft vasculopathy, currently available revascularisation methods and retransplantation are not appropriate options. Antiproliferative agents could provide significant improvement in terms of symptom relief and prognosis, but their definite value must be proven in well-designed trials.

Contemporary concepts in prevention and treatment of cardiac allograft vasculopathy

Cardiac allograft vasculopathy (CAV), is characterized by heterogeneous proliferative thickening of the vascular intima of the cardiac allograft vasculature. Since its presentation is commonly clinically silent, early diagnosis and preventative therapy are critical. Preventative therapy including optimization of immunosuppressive therapy and treatment of comorbidities associated with CAV progression must be initiated early since most of the intimal thickening occurs during the first year posttransplant. Long-term use of calcineurin inhibitors is associated with a high incidence of chronic renal disease and also contributes to hyperlipidemia and hypertension, all of which may exacerbate CAV. In addition, statins, antihypertensive agents and anti-CMV agents all have demonstrated benefits in reducing CAV. Once established, the limited treatment options include nonpharmacologic interventions such as retransplantation, percutaneous coronary interventions, coronary artery bypass grafting, transmyocardial laser revascularization and heparin-induced/mediated extracorporeal LDL plasmapheresis (HELP). As the use of new assessment tools increases our understanding of this disease, better preventative and treatment strategies are evolving.

Homocysteine-lowering therapy and early progression of transplant vasculopathy: a prospective, randomized, IVUS-based study

Although observational studies suggest that hyperhomocysteinemia may be a risk factor for coronary allograft vasculopathy (CAV), prospective data on homocysteine-lowering interventions and CAV development are lacking. We, therefore, randomized 44 de novo heart transplant (HT) recipients to 15 mg/day of 5-methyl-tetrahydrofolate (n=22), or standard therapy (control group, n=22) to investigate the effect of homocysteine lowering on the change in coronary intimal hyperplasia during the first 12 months after transplant, as detected by intra-vascular ultrasound (IVUS). Although 12 months after HT, homocysteinemia was lower in folate-treated patients (p<0.001), coronary intimal area increased similarly in the two groups (p>0.4). Conversely, hypercholesterolemia and cytomegalovirus infection were both associated with increased intimal hyperplasia (p<0.04), independently from folate intake. Sub-group analysis revealed that folate therapy reduced intimal hyperplasia in patients with hyperhomocysteinemia before randomization (n=19; p=0.02), but increased intimal hyperplasia in patients with normal homocysteine plasma concentrations (p=0.02). This bimodal effect of folate therapy persisted significantly after adjusting for cytomegalovirus infection and hypercholesterolemia. Despite effective in prevent hyperhomocysteinemia after heart transplantation, folate therapy does not seem to affect early CAV onset. However, sub-group analysis suggests that folate therapy may delay CAV development only in patients with baseline hyperhomocysteinemia, while may favor CAV progression in recipients with normal baseline homocysteinemia.

Increased plasma homocysteine concentrations accelerate cardiac allograft vasculopathy

BACKGROUND

A toxic and pro-oxidative effect of homocysteine on the coronary endothelium may accelerate cardiac allograft vascular disease (CAVD). In this study, we evaluated the influence of hyperhomocysteinemia on the course of CAVD.

METHODS

We investigated plasma homocysteine (tHCY) concentrations in 183 consecutive heart transplant recipients (158 men and 25 women, mean aged 53.1 +/- 10.0 years, at 6.7 +/- 3.2 years after transplantation) to evaluate the course of CAVD. We used serial coronary angiography to assess coronary status and graded the severity of CAVD based on the extent of luminal obstruction in the main coronary arteries (graded as 1-4). We defined progression as increased focal stenosis of >/=30% or as detection of a new coronary lesion after a mean observation period of 2.8 +/- 1.0 years. A multivariate analysis (backward logistic regression) was performed that included potential risk factors for CAVD. We excluded patients undergoing dialysis.

RESULTS

Initially, tHCY concentrations were increased in the entire cohort (mean, 18.6 +/- 7.6 mumol/liter) and ranged from 6.6 to 46.9 mumol/liter. A total of 105 patients (57.0%) had CAVD at first angiography, and progression was detected in 52 transplant recipients (28.0%). Patients with progressive CAVD had significantly greater tHCY concentrations (21.6 +/- 6.2 mumol/liter) at baseline investigation compared with patients who had stable courses (17.4 +/- 7.7 mumol/liter; p < 0.001). These results were independent of parameters such as sex, age, dyslipoproteinemia, cyclosporine blood concentrations, and indication for transplantation.

CONCLUSIONS

Progression of CAVD is strongly associated with increased tHCY concentrations. The intervals between routine surveillance angiography should be shortened in patients with hyperhomocysteinemia, and routine medical treatment to decrease homocysteine concentrations should be considered.

Treatment of hyperhomocysteinemia in pediatric heart transplant recipients

BACKGROUND

Graft coronary artery vasculopathy is the main cause of late morbidity and mortality in pediatric cardiac allograft recipients. Growing evidence suggests that elevated plasma homocysteine levels are associated with cardiac allograft vasculopathy following heart transplantation. The purpose of this study was to evaluate the effect of vitamin supplementation as a potential strategy for reducing homocysteine levels in pediatric heart transplant recipients and examine creatinine levels as potential determinants of plasma homocysteine concentration after transplantation.

METHODS

We studied 27 pediatric heart transplant patients with homocysteine levels higher than normal. All children received vitamin supplementation (vitamin B(12), vitamin E, vitamin A and folic acid). During treatment, levels of homocysteine, vitamins and creatinine were evaluated after 3, 6, 9 and 12 months.

RESULTS

We observed a significant homocysteine concentration decrease after treatment at every determination, whereas no significant change occurred for creatinine. Vitamin B(12) serum level increased markedly, whereas folic acid, vitamin E and vitamin A serum levels showed only minor increases.

CONCLUSIONS

We observed a significant increase of mean levels of vitamin B(12) and a moderate increase in the other 3 vitamins. We also observed a significant reduction in homocysteine levels, which returned to normal levels for age. In our patients, there was a correlation, before and after treatment, between homocysteine and creatinine levels, but there was no a direct correlation between creatinine serum levels and homocysteine reduction. We conclude that vitamin supplementation reduces and may normalize homocysteine serum level after pediatric heart transplantation.

Hyperhomocysteinemia and transplant coronary artery disease

BACKGROUND

Transplant coronary artery disease (TCAD) is a major cause of morbidity and mortality among heart transplant recipients. A variety of immunologic and nonimmunologic mechanisms are involved in the pathogenesis of the disease. Hyperhomocysteinemia has been recognized as an important risk factor for atherosclerotic vascular disease. The purpose of this article is to evaluate the prevalence of hyperhomocysteinemia in heart transplant recipients but more specifically to assess the published literature regarding the association between hyperhomocysteinemia and TCAD.

METHODS

A MEDLINE search using the key words hyperhomocysteinemia, transplant coronary artery disease, and heart transplant was performed.

RESULTS

Hyperhomocysteinemia has been commonly found among heart transplant recipients (average prevalence 51% to 76%). Worsening renal function and impaired vitamin metabolism seem to be the major causes of hyperhomocysteinemia in this particular population. TCAD has been found to be more prevalent and severe among patients with higher serum homocysteine levels. Vitamin supplementation is safe and effective in reducing serum homocysteine among heart transplant recipients.

CONCLUSION

A large, long-term, double-blind, placebo-controlled prospective trial aimed at assessing the clinical significance of homocysteine-lowering therapy on the natural history of TCAD seems warranted.