It is proposed that various pathologies can be explained, at least in part, by overproduction and lack of degradation of H2O2 (tumorigenesis, myxedematous cretinism, and thyroiditis) and by failure of the H2O2 generation or its positive control system (congenital hypothyroidism).

DNA double-strand breaks (DSBs) are considered as one of the primary causes of cancer but their induction by hydrogen peroxide (H 2 O 2 ) is still controversial. In this work, we studied whether the high levels of H 2 O 2 produced in the thyroid to oxidize iodide could induce DNA modifications. Scores of DNA damage, in terms of strand breaks, were obtained by comet assay (alkaline condition for single-strand breaks (SSBs) and neutral condition for DSBs). We demonstrated that in a rat thyroid cell line (PCCl3), non-lethal concentrations of H 2 O 2 (0.1-0.5 mmol/l) as well as irradiation (1-10 Gy) provoked a large number of SSBs (w2-3 times control DNA damage values) but also high levels of DSBs (1.2-2.3 times control DNA damage values). We confirmed the generation of DSBs in this cell line and also in human thyroid in primary culture and in pig thyroid slices by measuring phosphorylation of histone H2AX. L-Buthionine-sulfoximine, an agent that depletes cells of glutathione, decreased the threshold to observe H 2 O 2 -induced DNA damage. Moreover, we showed that DNA breaks induced by H 2 O 2 were more slowly repaired than those induced by irradiation. In conclusion, H 2 O 2 causes SSBs and DSBs in thyroid cells. DSBs are produced in amounts comparable with those observed after irradiation but with a slower repair. These data support the hypothesis that the generation of H 2 O 2 in thyroid could also play a role in mutagenesis particularly in the case of antioxidant defense deficiency.

We propose that high H2O2 production in thyrocytes is matched with specific transcriptionally regulated antioxidant protection.

Background: Metyrapone is a steroidogenesis inhibitor approved in Europe for the treatment of endogenous Cushing’s syndrome (CS) based on observational retrospective studies published over more than 50 years. We present data from the first prospective study designed to confirm metyrapone efficacy and good tolerance in patients with CS. Methods: This single arm, open-label, multicenter, international trial enrolled 50 patients with CS who had three baseline 24 hours urine free cortisol (UFC) values at least 50% above the upper limit of normal (ULN=165 nmol/24h). Metyrapone was titrated over 12 weeks (W12) to achieve normal urine (mean of 3 values, mUFC) and serum cortisol levels. Patients whose mUFC did not exceed 2-fold the ULN could enter a 6-month extension period. The primary efficacy endpoint was the proportion of patients with mUFC ≤ ULN at W12 assessed in a central laboratory using LC-MS/MS. The most important secondary endpoint was mUFC decrease of ≥ 50% at W12. Results: At baseline: mean age was 47 years, median mUFC (range) was 570 (291 - 8476) nmol/24h (3.5 x ULN). Hypercortisolism was in 96% of patients either moderate (mUFC ≥ 2xULN; < 5x ULN) in 63% or severe (≥5 x ULN) in 33%. Hypertension (69%) and diabetes mellitus (47%) were the most common comorbidities. At W12: 47% (23/ 49) met primary endpoint. Another 40% (19 / 49) had mUFC ≤ 2xULN. Median percentage decrease in mUFC from baseline to W12 was -74%. Secondary endpoint was met by 80% of patients who had a mUFC decrease of 50%. Final median metyrapone dose was 1500 (250; 5500) mg/day. Physical signs and symptoms were normalized or improved in 66% of patients. Circulating cholesterol, HbA1C and fasting glucose and insulin improved with median decrease of 12%, 3%, 5% and 9% respectively and median systolic and diastolic blood pressure also decreased by 4 and 5mmHg respectively. Among patients with antihypertensive treatments, 10 (31%) had a decrease in number of drugs and 5 (16%) had an increase in number of drugs during the study. Median ACTH increased by 11 % from baseline. Twenty six (52%) patients experienced mild to moderate study drug related adverse events (AEs). One patient discontinued before W12 because of an unrelated SAE on day 2 (pneumonia with septic shock). The most common AEs were nausea (24%), decreased appetite (18%), fatigue (14%), headache (10%), peripheral edema (6.0%), hypokalemia (6.0%) and hypertension (6.0%). Reversible adrenal insufficiency occurred in 6 (12%) patients. Few patients 14% (7/50) experienced at least one AE that led to a dose interruption or dose adjustment. Cushing Quality of Life Questionnaire increased of 10 points from baseline which is close to minimal clinically important difference = 10.1. Conclusions: This prospective study in patients with CS confirms that metyrapone effectively lowers UFC levels with a tolerability profile similar to the previously reported safety profile and improves QoL, at Week 12.