Aldosterone Synthase Promoter Polymorphism Predicts Outcome in African Americans With Heart Failure

Ethnic differences in proximal and distal tubular sodium reabsorption are heritable in black and white populations

BACKGROUND

Segmental handling of sodium along the proximal and distal nephron might be heritable and different between black and white participants.

METHODS

We randomly recruited 95 nuclear families of black South African ancestry and 103 nuclear families of white Belgian ancestry. We measured the (FENa) and estimated the fractional renal sodium reabsorption in the proximal (RNaprox) and distal (RNadist) tubules from the clearances of endogenous lithium and creatinine. In multivariable analyses, we studied the relation of RNaprox and RNadist with FENa and estimated the heritability (h) of RNaprox and RNadist.

RESULTS

Independent of urinary sodium excretion, South Africans (n = 240) had higher RNaprox (unadjusted median, 93.9% vs. 81.0%; P < 0.001) than Belgians (n = 737), but lower RNadist (91.2% vs. 95.1%; P < 0.001). The slope of RNaprox on FENa was steeper in Belgians than in South Africans (-5.40 +/- 0.58 vs. -0.78 +/- 0.58 units; P < 0.001), whereas the opposite was true for the slope of RNadist on FENa (-3.84 +/- 0.19 vs. -13.71 +/- 1.30 units; P < 0.001). h of RNaprox and RNadist was high and significant (P < 0.001) in both countries. h was higher in South Africans than in Belgians for RNaprox (0.82 vs. 0.56; P < 0.001), but was similar for RNadist (0.68 vs. 0.50; P = 0.17). Of the filtered sodium load, black participants reabsorb more than white participants in the proximal nephron and less postproximally.

CONCLUSION

Segmental sodium reabsorption along the nephron is highly heritable, but the capacity for regulation in the proximal and postproximal tubules differs between whites and blacks.

Using genetic information to select treatment for patients with heart failure: has the time come?

Personalized medicine is the concept of patient care becoming individualized based on distinctive characteristics. Pharmacogenetics is an application of personalized medicine, which may allow us to predict response to treatment based on an individual's genetic makeup. While several therapeutic areas have made significant advances in using pharmacogenetics to tailor therapies, it is not yet widely used in the treatment of heart failure. In this review, we summarize some of the emerging data on the use of pharmacogenetics in heart failure therapies.

Genomics, transcriptional profiling, and heart failure

Associated with technological progress in deoxyribonucleic acid and messenger ribonucleic acid profiling, advances in basic biology have led to a more complete and sophisticated understanding of interactions among genes, environment, and affected tissues in the setting of complex and heterogeneous conditions such as heart failure (HF). Ongoing identification of mutations causing hereditary hypertrophic and dilated cardiomyopathies has provided both pathophysiological insights and clinically applicable diagnostics for these relatively rare conditions. Genotyping clinical trial participants and genome-wide association studies have accelerated the identification of much more common disease- and treatment-modifying genes that explain patient-to-patient differences that have long been recognized by practicing clinicians. At the same time, increasingly detailed characterization of gene expression within diseased tissues and circulating cells from animal models and patients are providing new insights into the pathophysiology of HF that permit identification of novel diagnostic and therapeutic targets. In this rapidly evolving field, there is already ample support for the concept that genetic and expression profiling can enhance diagnostic sensitivity and specificity while providing a rational basis for prioritizing alternative therapeutic options for patients with cardiomyopathies and HF. Although the extensive characterizations provided by genomic and transcriptional profiling will increasingly challenge clinicians' abilities to utilize complex and diverse information, advances in clinical information technology and user interfaces will permit greater individualization of prevention and treatment strategies to address the HF epidemic.

Race-based therapeutics

The issue of race in medicine is problematic. Race is not a physiologic grouping, and all persons of a given race do not necessarily share the same clinical phenotype or genetic substrate. Despite clear signals that certain risk factors and diseases vary as a function of race, translating those differences into race-based therapeutics has been awkward and has done little to change the natural history of cardiovascular disease as it affects special populations. Among the varied special populations, the African American population appears to have the most significant and adverse variances for cardiovascular disease as well as worrisome signals that drug responsiveness varies. Recent guideline statements have now acknowledged certain treatment options that are most appropriate for African Americans with cardiovascular disease, especially hypertension and heart failure. As more physiologic markers of disease and drug responsiveness become available, the need for racial designations in medicine may lessen, and therapies can be optimized for all patients without regard to race or ethnicity.

The human G147D-protein phosphatase 1 inhibitor-1 polymorphism is not associated with altered clinical characteristics in heart failure

OBJECTIVES

A human protein phosphatase inhibitor-1 polymorphism, G147D (c.440G>A, p.147G>D), has been previously demonstrated to blunt the contractile responses of cardiomyocytes to beta-adrenergic agonists. The present study sought to examine whether the G147D inhibitor-1 polymorphism may be associated with specific clinical characteristics of heart failure carriers.

METHODS

Clinical information of 963 heart failure patients was analyzed according to race, inhibitor-1 genotype, treatment with beta-blockers and mortality patterns.

RESULTS

The G147D inhibitor-1 genetic variant was found almost exclusively in black subjects and its frequency was similar between normals and heart failure patients, indicating that it was not a primary risk factor for developing heart failure. Comparison of the major cardiac functional parameters and transplant-free survival patterns between carrier and noncarrier patients did not reveal any significant differences. Furthermore, echocardiographic evaluation showed similar outcomes of beta-blocker treatment between G147D carriers and noncarriers.

CONCLUSIONS

The present findings indicate that the human inhibitor-1 G147D polymorphism, found almost exclusively in blacks, may act as a modifier rather than risk factor in heart failure development.

Aldosterone synthase gene polymorphism as a determinant of atrial fibrillation in patients with heart failure

We analyzed the possible association between aldosterone synthase (CYP11B2) T-344C polymorphism, which is associated with increased aldosterone activity, and the prevalence of atrial fibrillation (AF) in 196 consecutive patients who had symptomatic systolic heart failure (HF; left ventricular ejection fraction <40%) for > or =3 months before recruitment. Genomic DNA was extracted from peripheral blood leukocytes using a standard protocol. Subjects were genotyped for the CYP11B2 polymorphism using the polymerase chain reaction/restriction fragment length polymorphism approach. AF was present in 63 patients (33%) with HF. We found the -344 CC genotype to be a strong independent marker for AF. Almost 1/2 (45%) of patients with this genotype had AF compared with 1/4 (27%) with -344 TT and TC genotypes (p = 0.01). A multivariate stepwise logistic regression model that included age, gender, New York Heart Association class, CYP11B2 -344CC genotype, and echocardiographic measurements of left ventricular ejection fraction, left atrial dimension, left ventricular end-diastolic diameter, and mitral regurgitation severity showed that the CYP11B2 CC genotype (adjusted for age and left atrial size) was an independent predictor of AF (adjusted odds ratio 2.35, 95% confidence interval 1.57 to 3.51, p = 0.03). In conclusion, CYP11B2 T-344C promoter polymorphism predisposes to clinical AF in patients with HF.

Pharmacogenetics of heart failure: evidence, opportunities, and challenges for cardiovascular pharmacogenomics

Heart failure is a significant medical problem affecting more than five million people in the USA alone. Although clinical trials of pharmacological agents have demonstrated significant reductions in the relative risk of mortality across populations, absolute mortality remains high. In addition, individual variation in response is great. Some of this variation may be explained by genetic polymorphism. In this paper, we review the key studies to date in heart failure pharmacogenetics, setting this against a background of recent progress in the genetics of warfarin metabolism. Several polymorphisms that have supporting molecular and clinical data in the heart failure literature are reviewed, among them the beta1-adrenergic receptor variant Arg389Gly and the angiotensin converting enzyme gene insertion/deletion polymorphism. These variants and others are responsible for a fraction of the total variation seen in the treatment response to heart failure. With the dawn of the genomic age, further pharmacogenetic and new pharmacogenomic studies will advance our ability to tailor the treatment of heart failure.

Usefulness of the aldosterone synthase gene polymorphism C-344-T to predict cardiac remodeling in African-Americans versus non-African-Americans with chronic systolic heart failure

A common polymorphism exists for the aldosterone synthase (CYP11B2) gene at position 344 (C-344-T). The 344-C allele has been associated with increased aldosterone synthase activity. We hypothesized that the aldosterone synthase gene polymorphism is associated with adverse cardiac remodeling in an ambulatory, chronic heart failure population. The CYP11B2 C-344T genotype was determined in 104 patients with heart failure who were in New York Heart Association classes I to IV, had left ventricular ejection fractions <40%, and were prospectively recruited from an urban heart failure clinic (65% African-American, 69% had a nonischemic cause, with a mean left ventricular ejection fraction of 22 +/- 9%). The 344-C allele frequency was 0.34 (45.2% TT, 42.3% CT, and 12.5% CC) and was significantly lower in African-American (0.27) versus Non-African-American patients (0.44, p = 0.018). Baseline and 1-year follow-up echocardiograms were obtained in 74 patients. Improvement was defined as a decrease in left ventricular end-systolic diameter (LVESD). At follow-up, the 344-C allele was associated with improved LVESD (p = 0.013). In addition, analysis by race showed that this effect was observed only in African-American patients (p <0.006). In multivariate logistic regression, controlling for cause, gender, and spironolactone use, the TT genotype (i.e., absence of 344-C allele) was associated with a fivefold lower rate of improvement in LVESD in African-Americans (p = 0.014). In conclusion, the 344-C allele of the aldosterone synthase gene polymorphism was associated with improved cardiac remodeling over time for African-Americans with chronic systolic heart failure. Although this genetic-driven increase in aldosterone activity should predispose to worse cardiac remodeling, it may represent a more susceptible state and enhanced response to therapy in this racial subgroup.

Race-related differences in heart failure therapies: simply black and white or shades of grey?

The magnitude of burden imposed by heart failure on society has necessitated the evolution of innovative strategies to identify specific avenues of treatment and the populations at highest risk. Multiple studies have demonstrated a higher burden of cardiovascular disease in black Americans. It has also been shown that the clinical characteristics of heart failure, therapeutic targets, and response to various treatment modalities, are different in blacks as compared with whites. This article explores the unique race-related differences in heart failure with particular emphasis on the currently recommended therapeutic agents in heart failure.