Primary Aldosteronism is the most common endocrine cause of hypertension. Unilateral disease in the form of Aldosterone producing adenomas (APAs) is found in 1.5-3% of hypertensive. Determining the source of aldosteronism is necessary for correct diagnosis and further molecular analysis.
To evaluate tissue aldosterone as a marker of aldosterone production and correlate it to patient phenotype and tumour mutation status, and to explore molecular heterogeneity in APAs.
Forty-six frozen tumour samples from patients diagnosed with APAs were included. Tumours were derived from a single endocrine referral center, and had been stored from 1985 to 2015. Tissue aldosterone concentration was related to clinical characteristics, genotype and molecular phenotype. Genetic heterogeneity was investigated by biopsies and in situ sequencing. Immunohistochemical analysis of Nephronectin, CYP11B1 and CYP11B2 were performed. qRT-PCR and in situ mRNA expression were used to analyze CYP11B2 mRNA expression.
Tissue aldosterone content was specific for aldosterone producing tumours and proved stable after long-term storage at -70C. CYP11B2 expression and aldosterone concentrations were higher in tumours with ATP1A1, ATP2B3 and CACNA1D mutations compared to those with KCNJ5 mutations (p<0.0001 and p=0.0018 respectively). The tissue aldosterone content correlated with CYP11B2 protein expression (r2=0.48, p<0.0001), and both CYP11B2 expression and tissue aldosterone content were associated with the plasma level of aldosterone (r2=0.33, p=0.0002 and r2=0.75, p<0.0001 respectively). In four tumours with suspicion of genetic heterogeneity, sampling of DNA revealed a heterogeneous KCNJ5 mutation in one tumour. Using in situ sequencing we confirmed heterogeneous expression of mutated KCNJ5 cDNA in the others. In three tumours classified as APAs, no mutation nor any aldosterone or CYP11B2 were detected, suggesting non-functional tumours.
Tissue aldosterone content is specific for aldosterone producing lesions, correlates with plasma levels, and displays variable levels depending on tumour genotype. Genetic heterogeneity is evident in a subgroup of KCNJ5 mutated tumours. The present results show that CYP11B2 expression and tissue aldosterone measurement may be used to clarify the source of aldosterone secretion.