Endocrine Abstracts

Background: Immune responses to self-peptides should not generally occur. However, four of 12 autoimmune Addison’s disease (AAD) patients developed adverse reactions immediately after synacthen injections, following repeated subcutaneous synacthen injections during a clinical trial (RoSA study). We wondered if these adverse effects were due to the production of anti-synacthen (ACTH_1–24) antibodies.

Methods: We evaluated the presence of serum anti-ACTH binding activity using immunoblotting and ELISA on sera from participants in the RoSA study (n=12; baseline and after synacthen exposure), 131 unrelated patients with AAD, 92 patients with Graves’ disease (GD), 15 patients with isolated ACTH deficiency and 102 controls without known autoimmune disease. Immunoblotting was performed on polyacrylamide/tricine gels using commercial synacthen and full-length ACTH peptide (both 10 μg/well). ELISA was performed using ACTH_1–24 (1 μg/ml) immobilised on solid phase.

Results: Bands at ~4 and ~6 kDa, corresponding to ACTH_1–24 and full-length ACTH_1–39 peptide respectively, were found in 10/12 (83%) RoSA study immunoblots, including all those who had an adverse reaction to synacthen. This is in contrast with healthy control sera, which showed no binding. The same 10 subjects from the RoSA study also showed high levels of binding to synacthen by ELISA, along with 28 patients with AAD (21% of 131), 13 patients with GD (14% of 92) and one isolated ACTH deficiency patient (7% of 15). All positive patient sera in the ELISA were tested against the synacthen peptide on immunoblotting, and all (n=41) showed specific 4kDa binding.

Conclusion: Our study demonstrates that repeated administration of depot synacthen can lead to anti-ACTH_1–24 autoreactivity. In addition, a significant number of AAD and GD patients also had similar autoreactivity (P<0.001). The presence of these antibodies could mediate some of the adverse effects seen in the RoSA study and explain the well-described phenomenon of resistance to chronic ACTH therapy.

Declaration of funding: This work was supported by the Medical Research Council (G0900001).