Decreased plasma prorenin levels in primary aldosteronism: potential diagnostic implications

Meta-analysis of blood parameters related to lipid and glucose metabolism between two subtypes of primary aldosteronism

It remains unclear whether metabolic profiles differ within the subtypes of primary aldosteronism (PA). This meta-analysis aimed to compare the blood parameters related to lipid and glucose metabolism at baseline between unilateral PA and bilateral PA. A search was performed using PubMed, Web of Science, and Sciencedirect databases, supplemented by hand-searching of related references. Standardized mean differences (SMDs) with 95% confidence intervals (CIs) were calculated for each parameter. Twenty-one studies involving 4197 patients with PA were included. Compared with bilateral PA groups, unilateral PA groups demonstrated significantly lower low-density lipoprotein cholesterol (LDL-C, SMD: -.14 mmol/L, 95% CI: -.20, -.07), total cholesterol (TC, SMD: -.16 mmol/L, 95% CI: -.23, -.09), triglyceride (TG, SMD: -.22 mmol/L, 95% CI: -.29, -.16), fasting blood glucose (FBG, SMD: -.11 mmol/L, 95% CI: -.18, -.04), hemoglobin A1c (HbA1c, SMD: -.21%, 95% CI: -.30, -.13), and homeostasis model assessment-insulin resistance (HOMA-IR, SMD: -.40, 95% CI: -.58, -.23). No significant difference was found in high-density lipoprotein cholesterol (HDL-C) level between the two groups (SMD: .40 mmol/L, 95% CI: -.02, .11). To sum up, comparison of several blood metabolic parameters between the two subtypes suggested that the bilateral PA may associate with a higher prevalence of impaired glucose and lipid metabolism than unilateral PA; however, results should be treated with caution. Additional well-designed studies are needed to prove the present results and better elucidate the link between metabolic abnormalities and etiologies of each PA subtype.

Impact of cortisol on blood pressure and hypertension-mediated organ damage in hypertensive patients

OBJECTIVES

Patients with overt and subclinical Cushing's syndrome frequently develop hypertension, metabolism disorders, and atherosclerotic lesions. The aim of the present study was to test the association between cortisol and blood pressure (BP), organ damage, and metabolic parameters in hypertensive patients without hypercortisolism.

METHODS

After exclusion of patients treated with corticosteroids or with Cushing's syndrome, the cohort included 623 hypertensive patients (mean ± SD age 50.3 ± 15.4 years, 50.9% men, median 24-h BP 146/88 mmHg) with an extended work-up (lipid profile, hypertension-mediated organ damage). Cortisol secretion was assessed by plasma cortisol at 0800 and 1600 h, and by 24-h urinary free cortisol (24 h UFC) normalized if required to urine creatinine (UFC/U creat).

RESULTS

Plasma cortisol at 1600 h, 24 h-UFC, and UFC/U creat were significantly and positively correlated with daytime, night-time, and 24-h SBP; plasma cortisol at 0800 h was not associated with BP. The strongest correlations were observed in the subgroup of aged more than 50 years (correlation coefficients between 0.23 and 0.28). These correlations remained after adjustment on plasma aldosterone. Metabolic parameters were weakly associated with cortisol. Arterial stiffness (central pulse pressure and pulse wave velocity), plasma NT-proBNP, and microalbuminuria were significantly correlated with 24 h UFC, UFC/U creat, and plasma cortisol at 1600 h.

CONCLUSION

Cortisol influences weakly the level of BP independently from plasma aldosterone in hypertensive patients, particularly in older patients, and that there was weak association with HMOD. It may, therefore, be of interest to test specific treatments targeting cortisol excess in selected hypertensive patients.

Human prorenin determination by hybrid immunocapture liquid chromatography/mass spectrometry: A mixed-solvent-triggered digestion utilizing D-optimal design

RATIONALE

Human prorenin, representing the precursor of mature renin, has been discussed as a potential biomarker, e.g. in diagnosing primary hyperaldosteronism or diabetes-induced nephropathy. Currently, only immunoassays are available for prorenin quantification. As the similarity of prorenin to active renin impedes its accurate determination by immunoassay, mass spectrometry appears as an accurate alternative for differentiation of that protein.

METHODS

Immunoaffinity purification plus a mixed-solvent-triggered digestion was combined with liquid chromatography/mass spectrometry (LC/MS) to enable a fast, sensitive, and less laboratory-intensive approach to the quantification of prorenin. Statistical experimental planning, which is known as Design of Experiments (DOE), was used to identify the optimal conditions for the generation of the signature peptides within a manageable number of experiments. The efficiency of the mixed-solvent-triggered digestion by trypsin was investigated using four different organic solvents: acetonitrile, acetone, tetrahydrofuran and methanol.

RESULTS

By utilizing a D-optimal design, we found that the optimal mixed-solvent type for the generation of both signature peptides was acetonitrile at a concentration of 84% and an incubation temperature of 16°C. Using the mixed-solvent-triggered digestion, the procedure time allowed a fast analysis of active renin and prorenin with a short digestion time of 98 min. This optimized mixed-solvent-triggered digestion procedure was applied to detect renin and prorenin successfully in human plasma by the newly developed hybrid approach.

CONCLUSIONS

The identification of unique surrogates for human prorenin enabled the mass spectrometric differentiation between the two similar proteins. The novel hybrid approach successfully proved its ability to purify, detect and distinguish between prorenin and active renin in human plasma.

Prorenin and active renin levels in paediatrics: a bioanalytical review

As part of the extended renin-angiotensin-aldosterone system, active renin and its precursor prorenin have been an area of research interest for decades. Although several studies showed a correlation with disease, other studies found no significant association, e.g. attributed to limited sample size or pharmacological effects of antihypertensive drugs. Since the measurement of both proteins has typically been carried out in adult populations, the data in paediatrics is limited. This review aimed to collate the current data on plasma renin and prorenin levels in children and compare the levels of healthy vs. the diseased state. A literature search using Medline resulted in 213 publications of which 15 studies were classified as relevant. In the extant studies in the literature, an age-dependent decline of renin plasma concentration was observed in newborns compared to adolescents. For children with cardiovascular disease, five studies were identified that provide limited insight into the pathophysiological regulation of renin. In general, sample handling is still a crucial step, which might particularly affect measured active renin concentrations due to conformational changes of its precursor prorenin. A reliable assessment for prorenin levels in the maturating population is yet not possible due to the low number of available publications. Three different approaches to quantify prorenin were found and raise the question on the comparability of these methods. The review emphazised several weaknesses and highlights the need for an accurate procedure to determine levels of active renin as well as prorenin in its closed and open form.

Clinical biomarker innovation: when is it worthwhile?

Background

Choosing which biomarker tests to select for further research and development is not only a matter of diagnostic accuracy, but also of the clinical and monetary benefits downstream. Early health economic modeling provides tools to assess the potential effects of biomarker innovation and support decision-making.

Methods

We applied early health economic modeling to the case of diagnosing primary aldosteronism in patients with resistant hypertension. We simulated a cohort of patients using a Markov cohort state-transition model. Using the headroom method, we compared the currently used aldosterone-to-renin ratio to a hypothetical new test with perfect diagnostic properties to determine the headroom based on quality-adjusted life-years (QALYs) and costs, followed by threshold analyses to determine the minimal diagnostic accuracy for a cost-effective product.

Results

Our model indicated that a perfect diagnostic test would yield 0.027 QALYs and increase costs by €43 per patient. At a cost-effectiveness threshold of €20,000 per QALY, the maximum price for this perfect test to be cost-effective is €498 (95% confidence interval [CI]: €275–€808). The value of the perfect test was most strongly influenced by the sensitivity of the current biomarker test. Threshold analysis showed the novel test needs a sensitivity of at least 0.9 and a specificity of at least 0.7 to be cost-effective.

Conclusions

Our model-based approach evaluated the added value of a clinical biomarker innovation, prior to extensive investment in development, clinical studies and implementation. We conclude that early health economic modeling can be a valuable tool when prioritizing biomarker innovations in the laboratory.

Mineralocorticoid and apparent mineralocorticoid syndromes of secondary hypertension

The mineralocorticoid aldosterone is a key hormone in the regulation of plasma volume and blood pressure in man. Excessive levels of this mineralocorticoid have been shown to mediate metabolic disorders and end-organ damage more than what can be attributed to its effects on blood pressure alone. Inappropriate excess levels of aldosterone contribute significantly to the cardiorenal metabolic syndrome and target organ injury that include atherosclerosis, myocardial hypertrophy, fibrosis, heart failure, and kidney disease. The importance of understanding the role of excess mineralocorticoid hormones such as aldosterone in resistant hypertension and in those with secondary hypertension should be visited. Primary aldosteronism is one of the commonly identified causes of hypertension and is treatable and/or potentially curable. We intend to review the management of mineralocorticoid-induced hypertension in the adult population along with other disease entities that mimic primary aldosteronism.