Low T3 syndrome occurs frequently in patients with sepsis. Type 3 deiodinase (DIO3) is present in immune cells, but there is no description of its presence in patients with sepsis. Here, we aimed to determine the prognostic impact of thyroid hormones levels (TH), measured on ICU admission, on mortality and evolution to chronic critical illness (CCI) and the presence of DIO3 in white cells. We used a prospective cohort study with a follow-up for 28 days or deceased. Low T3 levels at admission were present in 86.5% of the patients. DIO3 was induced by 55% of blood immune cells. The cutoff value of 60 pg/mL for T3 displayed a sensitivity of 81% and specificity of 64% for predicting death, with an odds ratio of 4.89. Lower T3 yielded an area under the receiver operating characteristic curve of 0.76 for mortality and 0.75 for evolution to CCI, thus displaying better performance than commonly used prognostic scores. The high expression of DIO3 in white cells provides a novel mechanism to explain the reduction in T3 levels in sepsis patients. Further, low T3 levels independently predict progression to CCI and mortality within 28 days for sepsis and septic shock patients.

Loss of muscle mass and strength is a common condition associated with adverse outcomes in critically ill patients. Here, we determined the correlation between non-thyroidal illness (NTIS) and molecular alterations in the muscle of critically ill individuals. We evaluated deiodinase expression, intramuscular triiodothyronine (T3) levels, and mitochondria and sarcoplasmic reticulum components. The cellular colocalization of the enzymes and its influence on myocytes and genes regulated by T3 were shown, including those of mitochondria. A prospective cohort of 96 patients. Blood and muscular samples were collected on admission to the intensive care unit (ICU), as well as clinical data and ultrasonographic measurements. Patients with NTIS showed increased oxidative stress markers associated with critical illness in muscle biopsy, such as carbonyl content and low sulfhydryl and GSH. The distribution pattern of deiodinases in muscle and its biochemical properties showed significant pathophysiological linkage between NTIS and muscle loss, as type 3-deiodinase (D3) was highly expressed in stem cells, preventing their differentiation in mature myocytes. Despite the high type 2-deiodinase (D2) expression in muscle tissue in the acute phase of critical illness, T3 was unmeasurable in the samples. In this scenario, we also demonstrated impaired expression of glucose transporters GLUT4, IRS1, and 2, which are involved in muscle illness. Here, we provide evidence that altered thyroid hormone metabolism contributes to stem cell dysfunction and further explain the mechanisms underlying critical illness-induced myopathy.

Background: Low T3 syndrome occurs frequently in patients with sepsis. Type 3 deiodinase (Dio3) is present in immune cells but there is no description of its presence in this patients. Here we aimed to determine the prognostic impact of thyroid hormones levels (TH) measured on ICU admission on mortality and on evolution to chronic critical illness (CCI) and the presence of D3 in white cells. Methods: Prospective cohort study with a follow-up for 28 days or deceased. Results: Low T3 levels at admission were present in 86.5% of the patients. Dio3 was 55% induced in immune cells. The cut-off value of 60 pg/mL for T3 displayed a sensitivity and specificity of 81% and 64% for predicting death, odds ratio of 4.89. Lower T3 yielded an area under the receiver operating characteristic curve of 0.76 and 0.75 for mortality and evolution to CCI, respectively, thus displaying better performance than commonly used prognostic scores. Conclusions: We advance in the pathophysiology of low T3 showing induced D3 in immune cells during sepsis. Low T3 levels independently predicted a progression to CCI and mortality within 28 days in sepsis and septic shock.