Proinflammatory/profibrotic effects of aldosterone in Gitelman's syndrome, a human model opposite to hypertension

PURPOSE

Aldosterone proinflammatory/profibrotic effects are mediated by the induction of mononuclear leucocytes (MNL) to express oxidative stress (OxSt)-related proteins, such as p22^phox, and by the activation of RhoA/Rho kinase pathway. Gitelman's syndrome (GS), an autosomal recessive tubulopathy, is an interesting opposite model to hypertension, being characterized by hypokalemia, activation of renin-angiotensin-aldosterone system yet normo/hypotension and lack of cardiovascular-renal remodeling. We aimed to evaluate the proinflammatory/profibrotic effect of aldosterone in MNL of 6 GS patients compared with 6 healthy subjects (HS).

METHODS

p22^phox expression and MYPT-1 phosphorylation status, a marker of RhoA/Rho kinase pathway activation, were evaluated in MNL of GS patients and HS at baseline and after incubation with aldosterone (1 × 10^-8 M) alone or with canrenone (1 × 10^-6 M).

RESULTS

At basal condition, p22^phox expression was significantly higher in HS than in GS patients (1.02 ± 0.05 densitometric unit (du) vs 0.40 ± 0.1 du, respectively). Aldosterone significantly increased p22^phox expression in HS and this effect was reversed by coincubation with canrenone (1.4 ± 0.05 du and 1.09 ± 0.03 du, respectively). No significant change was reported in GS after incubation of MNL with aldosterone and/or canrenone compared with basaline. Even MYPT-1 phosphorylation was significantly higher in HS compared with GS patients at basal condition (1.16 ± 0.1 du vs 0.69 ± 0.07, respectively). Aldosterone significantly increased MYPT-1 phosphorylation only in HS (1.37 ± 0.1 du vs 0.83 ± 0.12 du in GS).

CONCLUSIONS

GS patients seem to be protected by the OxSt status induced by aldosterone and revealed in HS. This human model could provide additional clues to highlight the proinflammatory/cardiovascular remodeling effects of aldosterone.

Gαq/p63RhoGEF interaction in RhoA/Rho kinase signaling: investigation in Gitelman's syndrome and implications with hypertension

PURPOSE

Gitelman's syndrome (GS) presents normo-hypotension and absence of cardiovascular-renal remodeling despite high angiotensin II (Ang II), activation of renin-angiotensin-aldosterone system and is a human model of endogenous antagonism of Ang II signaling, opposite to hypertension. GS's clinical presentation leads to questions regarding what features might be responsible. One area of investigation involves Ang II signaling. In hypertensive patients, RhoA/Rho kinase (RhoA/ROCK) pathway activation by Ang II is involved in hypertension development/maintenance and induction of long-term consequences (cardiovascular-renal remodeling), while GS has reduced p63RhoGEF gene and protein levels and ROCK activity. Ang II signaling is mediated by Gαq, which interacts with p63RhoGEF via the α6-αN linker connecting p63RhoGEF's DH and PH domains acting as a conformational switch to activate RhoA/ROCK signaling.

METHODS

We have investigated in GS patients, the presence of mutations in either p63RhoGEF's α6-αN linker domain and in Gαq's Ala253, Trp263, and Tyr356 residues, crucial for p63RhoGEF-Gαq interplay.

RESULTS

No mutations have been found in specific aminoacids of p63RhoGEF α6-αN linker and Gαq, key for p63RhoGEF/Gαq interplay.

CONCLUSIONS

Gitelman's syndrome normo/hypotension and lack of cardiovascular-renal remodeling are not due to mutations of p63RhoGEF α6-αN linker and Gαq interactions. This opens the way for investigations on different coding and no-coding regions (p63RhoGEF and Gαq promoters) and on altered transcriptional/post-transcriptional regulation. Clarification of how these biochemical/molecular mechanisms work/interact would provide insights into mechanisms involved in the GS's Ang II signaling fine tuning, in human physiology/pathophysiology in general and could also identify significant targets for intervention in the treatments of hypertension.

Collaborative meta-analysis of individual participant data from observational studies of Lp-PLA2 and cardiovascular diseases

BACKGROUND

A large number of observational epidemiological studies have reported generally positive associations between circulating mass and activity levels of lipoprotein-associated phospholipase A2 (Lp-PLA2) and the risk of cardiovascular diseases. Few studies have been large enough to provide reliable estimates in different circumstances, such as in different subgroups (e.g., by age group, sex, or smoking status) or at different Lp-PLA2 levels. Moreover, most published studies have related disease risk only to baseline values of Lp-PLA2 markers (which can lead to substantial underestimation of any risk relationships because of within-person variability over time) and have used different approaches to adjustment for possible confounding factors.

OBJECTIVES

By combination of data from individual participants from all relevant observational studies in a systematic 'meta-analysis', with correction for regression dilution (using available data on serial measurements of Lp-PLA2), the Lp-PLA2 Studies Collaboration will aim to characterize more precisely than has previously been possible the strength and shape of the age and sex-specific associations of plasma Lp-PLA2 with coronary heart disease (and, where data are sufficient, with other vascular diseases, such as ischaemic stroke). It will also help to determine to what extent such associations are independent of possible confounding factors and to explore potential sources of heterogeneity among studies, such as those related to assay methods and study design. It is anticipated that the present collaboration will serve as a framework to investigate related questions on Lp-PLA2 and cardiovascular outcomes.

METHODS

A central database is being established containing data on circulating Lp-PLA2 values, sex and other potential confounding factors, age at baseline Lp-PLA2 measurement, age at event or at last follow-up, major vascular morbidity and cause-specific mortality. Information about any repeat measurements of Lp-PLA2 and potential confounding factors has been sought to allow adjustment for possible confounding and correction for regression dilution. The analyses will involve age-specific regression models. Synthesis of the available observational studies of Lp-PLA2 will yield information on a total of about 15 000 cardiovascular disease endpoints.

Mechanistic approach to the pathophysiology of target organ damage in hypertension from studies in a human model with characteristics opposite to hypertension: Bartter's and Gitelman's syndromes

INTRODUCTION

Extensive studies using Bartter's/Gitelman's syndrome patients have provided insights into the angiotensin II (Ang II) signaling pathways involved in the regulation of vascular tone and cardiovascular-renal remodeling. The renin-angiotensin-aldosterone system is activated in these syndromes, however, patients do not develop hypertension and cardiovascular remodeling and clinically manifest conditions opposite to hypertension. The short- and the long-term signaling of Ang II remains an important matter of investigation to shed light on mechanisms responsible for the pathophysiology of hypertension and its long-term complications. The long-term signaling of Ang II is involved in the pathophysiology of cardiovascular-renal remodeling and inflammatory responses in which the balance between RhoA/Rho kinase pathway and NO system plays a crucial role.

METHODS AND RESULTS

In this brief review, the results of our studies in Bartter's and Gitelman's syndromes are reported on these processes.

CONCLUSIONS

The information obtained from these studies can clarify, confirm or be used to extend the biochemical mechanisms responsible for the pathophysiology of hypertension and its long-term complications and could offer further chances to identify additional potential significant targets of therapy.

Low plasma adiponectin is associated with coronary artery disease but not with hypertension in high-risk nondiabetic patients

OBJECTIVE

To investigate the association of plasma adiponectin levels with coronary artery disease (CAD), arterial hypertension (HT), and insulin resistance (IR) in nondiabetic Caucasian patients.

DESIGN

We measured plasma adiponectin levels, IR (HOMA index), and the CAD atherosclerotic burden (angiography-based modified Duke Index score) in 400 nondiabetic patients undergoing coronary angiography. HT was diagnosed by the European Society of Hypertension/European Society of Cardiology (ESH/ESC) guidelines or if patients were on antihypertensive treatment.

RESULTS

Coronary artery disease was found in 62% of the patients and ruled out in the rest (non-CAD group). Plasma adiponectin levels were inversely related to the CAD score (beta = -0.12, P = 0.029) and predicted the coronary atherosclerotic burden independent of other cardiovascular risk factors. However, they were similar in NT and HT and showed no correlation with blood pressure values. In non-CAD, but not in CAD patients, they were lower in patients with than without IR (8.3 +/- 1.2 vs. 11.3 +/- 1.3, respectively; P = 0.007).

CONCLUSIONS

In nondiabetic high-risk Caucasian patients plasma adiponectin levels are inversely related to CAD severity and IR; however, they are not strongly related to blood pressure values.

Relationship of early carotid artery disease with lipoprotein (a), apolipoprotein B, and fibrinogen in asymptomatic essential hypertensive patients and normotensive subjects

BACKGROUND

We investigated the relationships between plasma lipids and lipoprotein fractions and carotid artery lesions (CAL) in 177 cerebro-vascularly asymptomatic subjects, of whom 107 were primary hypertensive patients and 70 normotensive controls.

METHODS

The prevalence and severity of CAL, as assessed by calculating a score of severity (score of CAL) and the maximal stenosis of both sides, as well as the intimal-medial thickness (IMT) were evaluated with a high-resolution echo-Doppler technique. We measured total serum cholesterol, triglycerides, low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol, lipoprotein (a) [Lp(a)], Apo (apolipoprotein)AI, ApoAII, ApoB, and fibrinogen.

RESULTS

Both the prevalence (59.4% vs 26.2%) and severity of sex- and age-adjusted and unadjusted CAL and IMT were significantly higher in hypertensive patients than in controls. Regression analysis showed different predictors of IMT and maximal stenosis. The variables that remained in the model were age, mean blood pressure (BP), and smoking for IMT; pulse pressure, known duration of hypertension (HT), fibrinogen, and ApoB for the score of CAL; and the last four variables along with age and mean BP for maximal stenosis. Furthermore, we identified a link between the atherogenic lipoprotein fractions Lp(a) and ApoB, fibrinogen and early carotid artery atherosclerotic changes.

CONCLUSIONS

The different correlates of IMT, CAL, and maximal degree of stenosis suggest that they reflect different events occurring in the arterial wall in response to aging, HT, and other risk factors, rather than simply different stages of the same atherosclerotic process.