The prevalence of a raised aldosterone–renin ratio (ARR) among new referrals to a hypertension clinic

Disruption of Circadian Rhythm Genes in Obstructive Sleep Apnea Patients-Possible Mechanisms Involved and Clinical Implication

Obstructive sleep apnea (OSA) is a chronic condition characterized by recurrent pauses in breathing caused by the collapse of the upper airways, which results in intermittent hypoxia and arousals during the night. The disorder is associated with a vast number of comorbidities affecting different systems, including cardiovascular, metabolic, psychiatric, and neurological complications. Due to abnormal sleep architecture, OSA patients are at high risk of circadian clock disruption, as has been reported in several recent studies. The circadian clock affects almost all daily behavioral patterns, as well as a plethora of physiological processes, and might be one of the key factors contributing to OSA complications. An intricate interaction between the circadian clock and hypoxia may further affect these processes, which has a strong foundation on the molecular level. Recent studies revealed an interaction between hypoxia-inducible factor 1 (HIF-1), a key regulator of oxygen metabolism, and elements of circadian clocks. This relationship has a strong base in the structure of involved elements, as HIF-1 as well as PER, CLOCK, and BMAL, belong to the same Per-Arnt-Sim domain family. Therefore, this review summarizes the available knowledge on the molecular mechanism of circadian clock disruption and its influence on the development and progression of OSA comorbidities.

Circadian clock-mediated regulation of blood pressure

Most bodily functions vary over the course of a 24h day. Circadian rhythms in body temperature, sleep-wake cycles, metabolism, and blood pressure (BP) are just a few examples. These circadian rhythms are controlled by the central clock in the suprachiasmatic nucleus (SCN) of the hypothalamus and peripheral clocks located throughout the body. Light and food cues entrain these clocks to the time of day and this synchronicity contributes to the regulation of a variety of physiological processes with effects on overall health. The kidney, brain, nervous system, vasculature, and heart have been identified through the use of mouse models and clinical trials as peripheral clock regulators of BP. The dysregulation of this circadian pattern of BP, with or without hypertension, is associated with increased risk for cardiovascular disease. The mechanism of this dysregulation is unknown and is a growing area of research. In this review, we highlight research of human and mouse circadian models that has provided insight into the roles of these molecular clocks and their effects on physiological functions. Additional tissue-specific studies of the molecular clock mechanism are needed, as well as clinical studies including more diverse populations (different races, female patients, etc.), which will be critical to fully understand the mechanism of circadian regulation of BP. Understanding how these molecular clocks regulate the circadian rhythm of BP is critical in the treatment of circadian BP dysregulation and hypertension.

Angiotensin-Converting Enzyme Inhibitors and Angiotensin Receptor Blockers in Hypertension Due to Primary Aldosteronism: A Case for Exclusion

Aldosterone antagonists are the mainstay of therapy in patients with hypertension due to primary aldosteronism. However, in our experience, these patients are sometimes placed on angiotensin-converting enzyme (ACE) inhibitors in accordance with guidelines applying to the general hypertensive population. We believe this practice is inappropriate because of the inability of ACE inhibitors to lower blood pressure in patients with low renin levels. Furthermore, pleiotropic effects of ACE inhibitors are unlikely to provide significant benefits in the absence of blood pressure reduction. Therefore, ACE inhibitors should be discouraged for the majority of patients with primary aldosteronism, even in the face of renal or cardiac disease.

The circadian clock in the kidney

Circadian variations in renal function were first described in the 19th century, and GFR, renal blood flow, urine production, and electrolyte excretion exhibit daily oscillations. These clinical observations are well established, but the underlying mechanisms that govern circadian fluctuations in kidney are not fully understood. Here we provide a brief overview of the machinery governing the circadian clock and examine the clinical and molecular evidence supporting a critical role for circadian rhythm in the kidney. There is a connection between BP oscillation and renal disease that supports the use of chronotherapy in the treatment of hypertension or correction of nondipping BP. Such studies support a developing model of clock controlled sodium and water transport in renal epithelial cells. Recent advances in identifying novel clock-controlled genes using rodent and cellular models also shed light on the molecular mechanisms by which the circadian clock controls renal function; however, the field is new and much more work remains.

Primary aldosteronism can alter peripheral levels of transforming growth factor beta and tumor necrosis factor alpha

Primary aldosteronism (PA) is the most common secondary cause of hypertension that has recently been implicated in alterations of the immune system and progression of cardiovascular disease.

OBJECTIVE

To study the cytokines transforming growth factor beta1 (TGF-beta1), tumor necrosis factor alpha (TNF-alpha), and interleukin 10 (IL-10) in patients with PA and essential hypertensives (EH) and evaluate its association with the renin-angiotensin-aldosterone system.

PATIENTS AND METHODS

We studied 26 PA and 52 EH patients as controls, adjusted by their blood pressure, body mass index, age, and gender. In both groups, PA and EH, we measured serum aldosterone (SA), plasma renin activity (PRA), and cytokines TGF- beta1, TNF-alpha, and IL-10. In addition, 17 PA patients were treated for 6 months with spironolactone, a mineralocorticoid receptor (MR) antagonist.

RESULTS

PA patients had lower levels of TGF-beta1 (17.6+/-4.1 vs 34.5+/-20.5 pg/ml, p<0.001) and TNF-alpha (17.0+/-4.4 vs 35.6+/-21.7 pg/ml, p<0.001) and similar IL-10 levels (99.7+/-18.7 vs 89.4+/-49.5 pg/ml, p: ns), as compared with EH controls. TGF-beta1 and TNF-alpha levels showed a remarkable correlation with SA/PRA ratio in the total group (PA+EH). The treatment of PA patients with spironolactone increased the TGF-beta1 levels (18.3+/-5.9 to 28.4+/-6.3 pg/ml, p<0.001), while TNF-alpha, and IL-10 remained unchanged.

CONCLUSION

Our results showed that PA patients have lower TGF-beta1 and TNF-alpha cytokine serum levels than EH. TGF-beta1 levels were restored with spironolactone, showing a MR-dependent regulation. In this way, the chronic aldosterone excess modifies the TGF-beta1 levels, which could produce an imbalance in the immune system homeostasis that may promote an early proinflammatory cardiovascular phenotype.

Aldosterone-receptor antagonism in hypertension

The role of the renin-angiotensin-aldosterone system (RAAS) in hypertension has since long been recognized and aldosterone has been acknowledged as one of the key hormones in the pathophysiology, not only in primary aldosteronism but also in essential hypertension and drug-resistant hypertension. Aldosterone-receptor antagonists (ARAs) are increasingly used in patients with resistant hypertension, often with impressive results. However, definitive evidence for the benefit of ARAs in these patients from randomized, controlled trials is lacking. This review gives an overview of the current data on this topic. Future studies should focus on the identification of factors that are able to predict the response to treatment, as to select patients who will benefit most from treatment with ARAs. On the basis of the current knowledge, we recommend prescription of ARAs to patients with primary aldosteronism, resistant hypertension and patients with hypertension and hypokalemia.

The circadian clock protein Period 1 regulates expression of the renal epithelial sodium channel in mice

The mineralocorticoid aldosterone is a major regulator of sodium transport in target epithelia and contributes to the control of blood pressure and cardiac function. It specifically functions to increase renal absorption of sodium from tubular fluid via regulation of the alpha subunit of the epithelial sodium channel (alphaENaC). We previously used microarray technology to identify the immediate transcriptional targets of aldosterone in a mouse inner medullary collecting duct cell line and found that the transcript induced to the greatest extent was the circadian clock gene Period 1. Here, we investigated the role of Period 1 in mediating the downstream effects of aldosterone in renal cells. Aldosterone treatment stimulated expression of Period 1 (Per1) mRNA in renal collecting duct cell lines and in the rodent kidney. RNA silencing of Period 1 dramatically decreased expression of mRNA encoding alphaENaC in the presence or absence of aldosterone. Furthermore, expression of alphaENaC-encoding mRNA was attenuated in the renal medulla of mice with disruption of the Per1 gene, and these mice exhibited increased urinary sodium excretion. Renal alphaENaC-encoding mRNA was expressed in an apparent circadian pattern, and this pattern was dramatically altered in mice lacking functional Period genes. These results suggest a role for Period 1 in the regulation of the renal epithelial sodium channel and more broadly implicate the circadian clock in control of sodium balance.