Endocrine Abstracts

Introduction: Primary Aldosteronism is the most common cause of secondary hypertension. First-line treatment; adrenalectomy resects adrenal nodules and adjacent normal tissue, limiting suitability to those who present with unilateral disease. Use of thermal ablation represents an emerging approach as a possible minimally invasive therapy for unilateral and bilateral disease, to target and disrupt hypersecreting aldosterone producing adenomas, while preserving adjacent normal adrenal cortex. Ablation involves heating tissue >50°C to induce cellular necrosis. Outside the core ablation zone, the transitional zone is an area exposed to variable temperatures between 37°C – 50°C. To understand the feasibility of precision ablation in the adrenal gland, we examined the effect of applying these temperatures to adrenocortical cells to identify i) the required temperature to effectively ablate adrenal cells ii) the extent of damage that may occur to surrounding healthy adrenal cells with exposure to transitional zone temperatures.

Methods: Steroidogenic adrenocortical cell lines, H295R and HAC15, were treated with hyperthermia (high precision water bath) at temperatures of 37, 42, 45, 48 and 50°C. Steroidogenesis was subsequently stimulated using forskolin (10μM) and angiotensin II (10 nM), or cells were treated with Thapsigargin (10uM). Cell death (Propidium iodide staining by flow cytometry), proliferation (xCELLigence real-time cell analysis), protein expression (Western blot/qRT-PCR), steroid secretion (HPLC-Mass spectrometry) and intracellular calcium release (Fluo-4 AM flow cytometry/confocal live imaging) were analysed immediately and 7-days post-treatment.

Results: Cell death occurred at 48°C and 50°C (P<0.05 vs 37°C control), but not 45°C, or 42°C. Sublethal hyperthermia (45°C for 30 minutes) induced a heat shock response (upregulated HSP70 and HSP90), alongside a decrease in aldosterone and cortisol secretion (P<0.05), reduced expression of steroidogenic enzymes (CYP11B1, CYP11A1)(P<0.05), and decreased intracellular calcium release 18-h post treatment. At 7-days post sublethal hyperthermia, steroid secretion and steroidogenic enzymatic expression returned to baseline levels.

Conclusion: Hyperthermia at 48°C and 50°C for 15 minutes is required for sustained cell death at 7-days post treatment. Sublethal hyperthermia, equivalent to that produced in the transitional zone during thermal ablation, produces a short-lived unsustained inhibition of steroidogenesis that recovers 7-days post treatment. Therefore, segmental adrenal sparing ablation is possible with recovery of transitional zone following ablation. This underlines the potential for precision technology development for bilateral adrenal ablation as definitive measure to treat PA caused by APA or Micronodular disease.