Tyrosine hydroxylase polymorphism (C-824T) and hypertension: a population-based study

Genetic Variations of Tyrosine Hydroxylase in the Pathogenesis of Hypertension

One of the major pathophysiological features of primary hypertension is an inappropriate activation of the sympathetic nervous system, which is mediated by excessive synthesis and secretion of catecholamine into the blood. Tyrosine hydroxylase (TH), a rate-limiting enzyme in the synthesis of catecholamine, has been highlighted because genetic variations of TH could alter the activity of the sympathetic nervous system activity and subsequently contribute to the pathogenesis of hypertension. Here, we discuss the role of TH as a regulator of sympathetic activity and review several studies that investigated the relationship between genetic variations of TH and hypertension.

Roles of catecholamine related polymorphisms in hypertension

The objective of this review is to summarize current data obtained so far in catecholamine-essential hypertension (EH) relationships on a genetic basis. As the major elements driving the sympathetic system’s actions, catecholamines modulate a variety of physiological processes and mutations related to the system. This could generate serious disorders, such as severe mental illnesses, stress-induced disorders, or impaired control of blood pressure or motor pathways. EH is idiopathic, and the genetic basis of its causes and substantial interindividual discrepancies in response to different types of treatments are the focus of interest. Susceptibility to disease or efficacy of treatments are thought to reflect genomic variabilities among individuals. Therefore, outlining the available knowledge in functional genetic polymorphisms linked to EH will make the picture clearer and will help to establish future prospects in the field.

Differential circadian catecholamine and cortisol responses between healthy women with and without a parental history of hypertension

OBJECTIVES

Previous studies suggest that otherwise healthy individuals who have a parental history of hypertension (PH+) have an accentuated reactive rise in catecholamines and cortisol to laboratory stressors as well as elevated plasma levels when compared with those with no parental history (PH-); however, few, if any, studies have evaluated whether parental history affects the responses of these hormones to changing environmental circumstances in everyday life. The purpose of this study was to compare urinary catecholamine (epinephrine and norepinephrine) and cortisol excretion and ambulatory blood pressures (BPs) across three daily microenvironments between women with and without a parental history of hypertension.

METHODS

The women in the study (PH+, N = 62, age = 35.2 ± 9.1; PH-, N = 72, age = 33.8 ± 10.0) worked in clerical, technical, or professional positions at a major medical center in New York City. Urinary hormone excretion rates and ambulatory BP were measured across three daily microenvironments: work (11 am to 3 p.m.), home (approximately 6 p.m. to 10 p.m.), and during sleep (approximately 10 p.m. to 6 a.m.). History group comparisons by microenvironment were made using repeated-measures ANCOVA and ANOVA analyses.

RESULTS

The results show that epinephrine excretion among PH+ women was 36% higher than PH- women (P < 0.008) over the entire day and that nocturnal cortisol excretion was also greater among PH+ women (P < 0.045). PH+ women also had statistically significantly higher systolic (4 mm Hg higher; P < 0.01) and diastolic (2 mm Hg higher, P < 0.03) BP when compared with PH- women across all daily microenvironments.

CONCLUSION

These findings suggest that there may be genetically linked mechanisms which elevate tonic epinephrine levels and nocturnal cortisol levels that contribute to elevating circadian BP.

The contribution of the C-824T tyrosine hydroxylase polymorphism to the prevalence of hypertension in a South African cohort: the SABPA study

The C-824T single nucleotide polymorphism in the promoter region of the tyrosine hydroxylase gene has been associated with hypertension. It is well documented that African South Africans exhibit a higher prevalence of hypertension than Caucasians. However, the possible role of this mutation on 24-hour ambulatory blood pressure (AMBP) has not been investigated in African South Africans. Blood samples of 409 South Africans were screened for the mutation. Ambulatory blood pressure and lifestyle factors were also measured. Africans had higher incidence of hypertension and higher occurrence of the mutation. However, the contribution of the tyrosine hydroxylase C-824T single nucleotide polymorphism to hypertension could not be confirmed in our cohort.

Disorders of blood pressure regulation-role of catecholamine biosynthesis, release, and metabolism

Catecholamines (epinephrine and norepinephrine) are synthesised and produced by the adrenal medulla and postganglionic nerve fibres of the sympathetic nervous system. It is known that essential hypertension has a significant neurogenic component, with the rise in blood pressure mediated at least in part by overactivity of the sympathetic nervous system. Moreover, novel therapeutic strategies aimed at reducing sympathetic activity show promise in the treatment of hypertension. This article reviews recent advances within this rapidly changing field, particularly focusing on the role of genetic polymorphisms within key catecholamine biosynthetic enzymes, cofactors, and storage molecules. In addition, mechanisms linking the sympathetic nervous system and other adverse cardiovascular states (obesity, insulin resistance, dyslipidaemia) are discussed, along with speculation as to how recent scientific advances may lead to the emergence of novel antihypertensive treatments.

The immune marker soluble urokinase plasminogen activator receptor is associated with new-onset diabetes in non-smoking women and men

AIM

To explore the putative association of new-onset diabetes and the soluble urokinase plasminogen activator receptor (suPAR), which is a new and stable plasma marker of immune function and low-grade inflammation. This association has been previously suggested by using the less sensitive International Classification of Disease system to detect incident diabetes in the Danish MONICA 10 cohort.

METHODS

The Danish National Diabetes Register enabled more accurate identification of incident diabetes during a median follow-up of 13.8 years in the Danish MONICA 10 cohort (n = 2353 generally healthy individuals). The soluble urokinase plasminogen activator receptor was measured by the ELISA method. To fulfil model assumptions, outcome analyses were stratified by age, and further by smoking, owing to the interaction between the soluble urokinase plasminogen activator receptor and smoking on new-onset diabetes (P < 0.0001).

RESULTS

New-onset diabetes (n = 182) was associated with increased soluble urokinase plasminogen activator receptor levels (P = 0.013). Among 699 middle-aged (41 and 51 years) and 564 older (61 and 71 years) non-smokers, participants in the upper soluble urokinase plasminogen activator receptor quartile had a sex- and age-adjusted relative risk of 6.01 (95% CI 2.17-16.6, P < 0.0006) and relative risk of 3.25 (95% CI 1.51-6.98, P = 0.0025), respectively, for new-onset diabetes compared with participants in the lowest quartile. This relationship remained significant after additional adjustments for C-reactive protein and leukocytes or fasting glucose and insulin or BMI (P < 0.05). The soluble urokinase plasminogen activator receptor was not related to incident diabetes among smokers (P ≥ 0.85).

CONCLUSIONS

In these explorative analyses, the soluble urokinase plasminogen activator receptor associated independently with incident diabetes in non-smokers, supporting an immune origin of Type 2 diabetes. Competing disease risk may explain lack of association among smokers.