Effects of aldosterone antagonism on microvascular function in obese individuals

The prevalence of obesity and obesity-related complications is currently taking
epidemic proportions. These complications increase the risk of type 2 diabetes
and cardiovascular disease, which are important causes of morbidity and
mortality worldwide.
It is important to gain insight in the mechanisms underlying obesity-related
complications, because this may lead to the development of directed therapeutic
strategies.
Currently, there is significant evidence that the cause of both insulin
resistance and hypertension must be sought at the level of the
microcirculation.
Over activity of the renin-angiotensin-aldosterone system is a potential cause
of microvascular dysfunction. Angiotensin II was indeed found to be implicated
in the pathogenesis of obesity-associated hypertension and insulin resistance,
possibly through interference with the vascular effects of insulin.
Increased aldosterone levels have also been associated with resistant
hypertension and insulin resistance, which is illustrated in patients with
primary aldosteronism. Furthermore, aldosterone is known to exert several
detrimental effects on the vasculature, some of which are offset by
mineralocorticoid receptor antagonists.
In obese individuals, plasma aldosterone concentrations are increased as well.
We hypothesize that increased aldosterone levels in adipose persons induce
microvascular dysfunction, which contributes to the development of insulin
resistance and hypertension, and mineralocorticoid receptor antagonism results
in improved insulin sensitivity and decreased blood pressure by counteracting
the adverse effects of aldosterone on the microvasculature.

Primary objectives:
1. Is plasma aldosterone concentration associated with microvascular function,
specifically insulin-mediated capillary recruitment, in obese subjects?
2. Does mineralocorticoid receptor antagonism result in improvement of
microvascular function, specifically insulin-mediated capillary recruitment,
and of insulin sensitivity, in obese subjects?

Secondary objectives:
1. Is plasma aldosterone concentration associated with vascular stiffness and
endothelial function in obese subjects?
2. Does mineralocorticoid receptor antagonism result in reduction of vascular
stiffness and improvement of endothelial function in obese subjects?

This is a randomized, double blind, placebo-controlled intervention study.

After screening for eligibility, participants will visite the study centre at
two days.
During the first day, baseline measurements of vascular function (endothelial
glycocalyx thickness, nailfold capillary microscopy, vasomotion analysis,
contrast enhanced ultrasound, determination of pulse wave velocity and carotid
distensibility, pulse wave analysis and peripheral arterial tonometry) will be
performed before and during a hyperinsulinemic, euglycemic clamp test.
A total amount of 180 mL blood will be drawn for determination of electrolytes,
renal and hepatic function, lipid profile, glucose, insulin, markers of
endothelial activation and inflammation, adipokines and components of the RAAS
system.
After the first study day, subjects will be randomized to treatment with either
50 mg Eplerenone during 4 weeks or placebo treatment.
At the end of the treatment period, all measurements of vascular function
performed during the first day will be repeated before and during a
hyperinsulinemic, euglycemic clamp, as well as the blood sampling.

30 obese individuals will be randomized to treatment with the selective
mineralocorticoid receptor antagonist Eplerenone, 50 mg once daily during 4
weeks. The remaining 30 obese individuals will be randomized to treatment with
a matched placebo during 4 weeks.

Participants will visit the study center 3 times: once for a screening visit,
and at two occasions for measurements of (micro)vascular function (baseline and
follow-up) during a hyperinsulinemic, euglycemic clamp test. For screening
purposes, 9 mL blood will be drawn to determine electrolytes, renal and hepatic
function, lipid profile and glucose. At study days, measurements of
(micro)vascular function will be performed in the fasting state, before and
during a hyperinsulinemic, euglycemic clamp test for determination of insulin
sensitivity. Participants will be requested to abstain from alcohol and not to
smoke 12 hours prior to the measurements, and not to perform strenuous exercise
48 hours prior to the study days.
The most prevailing side effect of the hyperinsulinemic euglycemic clamp test
is hypoglycemia. Measurements of (micro) vascular function include
determination of endothelial glycocalyx thickness, skin capillary microscopy,
skin vasomotion analysis (basal and during local heating), contrast-enhanced
ultrasound of skeletal muscle, determination of carotid distensibility and
carotid femoral pulse wave velocity, pulse wave analysis, and peripheral
arterial tonometry, and are merely noninvase. The contrast agent administered
during contrast-enhanced ultrasound of skeletal muscle has proven to be a safe
imaging modality in previous investigations.
During both visits, a total amount of ~ 180 mL blood is drawn for determination
of electrolytes, renal function, lipid profile, insulin, markers of endothelial
activation and inflammation, RAAS components, and glucose values during the
hyperinsulinemic, euglycemic clamp. This amount of blood carries no risks for
the participants.
One week before baseline measurements, participants will be started on a
moderately-low sodium diet, which is continued throughout the study (5 weeks
total). Prior to baseline measurements, antihypertensive therapy (if
participants are receiving any) will be temporarily ceased. This is not
expected to cause health concerns.
After baseline measurements of (micro)vascular function, participants will be
randomized to treatment with either Eplerenone or a matched placebo during 4
weeks. Common side effects of Eplerenone include gastro-intestinal complaints,
hypotension, hyperkalemia and impaired renal function. Blood pressure,
potassium values, and renal and hepatic function will be monitored following
the first week of treatment. After 4 weeks, all measurements of (micro)vascular
function will be repeated.
Short-term treatment with Eplerenone will not be of sustained benefit for the
participating subjects; subjects who are randomized to placebo treatment will
obtain no health benefit at all. Furthermore, the sodium-restricted diet and
the treatment with either Eplerenone or placebo demand a strict compliance from
the participant. The amount of time invested is also considerable and a large
amount of measurements will be performed (determination of (micro)vascular
function, laboratory investigations, 24h blood pressure measurements).
This burden on the participants is justified, however, since we might elucidate
mechanisms leading to obesity-related complications, which possess a major
health risk. Participants will also gain insight into their own risk profile
for the development of type 2 diabetes and cardiovascular disease.
All subjects will receive a compensation of ¤ 300,- after completion of the
study.
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