EN01 - Expression of Steroidogenic Enzymes in Canine Functional and Non-functional Adrenocortical Tumours

Abstract: Background
Functionality of human adrenal tumours is inferred by CYP11B1 (cortisol synthase) and/or CYP11B2 (aldosterone synthase) expression. However, dogs have a single multi-functional CYP11B enzyme so alternative strategies are required to interrogate functionality. It has been proposed CYP17 expression controls production of cortisol, rather than aldosterone, by adrenocortical cells in dogs.

Hypothesis/Objectives
Non-functional canine adrenal tumours will have low expression of steroidogenic enzymes, while aldosterone-producing tumours express CYP11B, and cortisol-producing tumours both CYP11B and CYP17.

Animals
17 dogs with adrenal tumours (8 non-functional, 7 cortisol-producing and 2 aldosterone-producing) and two with normal adrenal glands.

Methods
Adrenal functionality was determined from clinical signs and endocrine testing. CYP11B and CYP17 expression were detected by immunohistochemistry on formalin-fixed paraffin-embedded adrenal tissue. Protein expression was semi-quantified by two blinded observers using H-scoring and compared in non-functional and cortisol-producing adrenal tumours using Mann-Whitney U tests. Results are reported as median [range].

Results
Normal adrenal zona glomerulosa was CYP11B positive, zona fasciculata and reticularis were CYP11B and CYP17 positive. Expression of CYP11B (190 [130-265] vs. 147.5 [95-202.5]; P=.07) and CYP17 (177.5 [87.5-240] vs. 247.5 [55-292.5]; P=.397) was not significantly different between cortisol-producing and non-functional canine adrenal tumours respectively. Expression of CYP11B (142.5, 230) and CYP17 (95, 220) in aldosterone-producing adrenal tumours was similar to that of the other tumours.

Conclusions and clinical importance
Retrospective determination of functionality of canine adrenal tumours using immunohistochemistry is difficult. The mechanisms for differential control of cortisol and aldosterone synthesis in species with a single CYP11B enzyme remain poorly understood.