Thyroid abnormalities in term infants with fungal sepsis

HPT axis‑independent TSHβ splice variant regulates the synthesis of thyroid hormone in mice

Thyroid stimulating hormone (TSH) consists of an α‑subunit and a unique β‑subunit. The first in‑frame TSHβ splice variant produced by the cells of immune system was identified in 2009. The TSHβ splice variant and native TSHβ exhibit different expression profiles, and research has been conducted to elucidate the role of the TSHβ splice variant in different diseases. However, understanding of the fundamental physiological characteristics of the TSHβ splice variant is currently limited. To verify whether the TSHβ splice variant has the potential to induce thyroid follicular cells to synthesize thyroid hormone, in vivo and in vitro stimulation experiments were conducted in the present study. A total of 60 C57BL/6 mice were divided into control‑, 5 and 10 µg TSHβ splice variant‑treated groups at random. Mice were sacrificed at 0.5, 1 and 4 h after intraperitoneal injection, and serum levels of tri‑iodothyronine (T3) and thyroxine (T4) were determined using a radioimmunoassay. Thyroid follicular cells were isolated from the thyroids of mice, and stimulated with 2 µg/ml TSHβ splice variant. Supernatants were collected, and the levels of T3 and T4 were detected. The protein expression levels of the sodium‑iodide symporter, thyroperoxidase and thyroglobulin in thyroid follicular cells were quantified using western blot analysis. To verify whether the TSHβ splice variant expression was regulated by the hypothalamus‑pituitary‑thyroid (HPT) axis, similar to native TSHβ, a total of 60 C57BL/6 mice were equally divided into control, 2 mg/kg T3 intraperitoneal injection and 0.05 mg/kg thyroid‑releasing hormone intraperitoneal injection groups at random. Mice were sacrificed at 1 and 4 h after injection. Alterations in the expression of the TSHβ splice variant in the pituitary, thyroid, peripheral blood leukocytes and spleen tissues were detected using western blot analysis. The present study demonstrated that the TSHβ splice variant is not regulated by the HPT axis and may affect thyroid hormone synthesis. Modifications in the expression of the TSHβ splice variant may occur in a uniquely regulated manner to provide peripheral immunological compartments with a source of activated cells, particularly under immune stress.

Thyroid function tests in patients at the emergency department compared to a prior healthy setting

We examined the changes in thyroid hormone levels in patients with an acute clinical condition and compared these to levels in the healthy subjects. Serum total triiodothyronine (T3), thyroid stimulating hormone (TSH), and free thyroxine (fT4) measurements were recorded from 555 patients (mean age: 55.0 years, men: 65.9%) admitted to the emergency department (ED) 1-91 months (median: 34 months) after a regular health examination (HE). Serological data were analyzed; mean change in hormone levels was stratified by emergency classification system and quintiles of changes in inflammatory marker values, such as neutrophil lymphocyte ratio (NLR) and high-sensitivity C-reactive protein (CRP). The mean decrease in T3 levels from HE and ED samples was 10.6 ng/dL (p< 0.001). Mean decrease in T3 levels was 21.6 ng/dL among patients classified as having an infection status and 11.0 ng/dL among patients classified as having an urgency status. A decrease 3.7 ng/dL among emergency patients was observed. TSH and fT4 levels did not change across all groups. When patients were stratified into quintiles according to changes in NLR values, mean decreases in T3 were 6.21, 8.14, 14.37, 12.76, and 21.98 ng/dL and showed significant linear reduction (p<0.001). For quintiles of changed CRP values, mean decreased T3 levels were 10.57, 3.05, 4.47, 7.68, and 28.07 ng/dL. TSH and fT4 were not associated with significant changes (p = 0.100, p = 0.561, respectively). In this study, thyroid function changes in individuals with an acute condition revealed that T3 significantly decreased, more markedly in infectious diseases compared to their healthy counterparts, and decline in T3 measurements correlated with inflammatory markers. TSH and fT4 levels remained stable. It is necessary to consider the severity of acute conditions when abnormal T3 levels are detected in subjects with emergent status.

Thyroid Allostasis-Adaptive Responses of Thyrotropic Feedback Control to Conditions of Strain, Stress, and Developmental Programming

The hypothalamus-pituitary-thyroid feedback control is a dynamic, adaptive system. In situations of illness and deprivation of energy representing type 1 allostasis, the stress response operates to alter both its set point and peripheral transfer parameters. In contrast, type 2 allostatic load, typically effective in psychosocial stress, pregnancy, metabolic syndrome, and adaptation to cold, produces a nearly opposite phenotype of predictive plasticity. The non-thyroidal illness syndrome (NTIS) or thyroid allostasis in critical illness, tumors, uremia, and starvation (TACITUS), commonly observed in hospitalized patients, displays a historically well-studied pattern of allostatic thyroid response. This is characterized by decreased total and free thyroid hormone concentrations and varying levels of thyroid-stimulating hormone (TSH) ranging from decreased (in severe cases) to normal or even elevated (mainly in the recovery phase) TSH concentrations. An acute versus chronic stage (wasting syndrome) of TACITUS can be discerned. The two types differ in molecular mechanisms and prognosis. The acute adaptation of thyroid hormone metabolism to critical illness may prove beneficial to the organism, whereas the far more complex molecular alterations associated with chronic illness frequently lead to allostatic overload. The latter is associated with poor outcome, independently of the underlying disease. Adaptive responses of thyroid homeostasis extend to alterations in thyroid hormone concentrations during fetal life, periods of weight gain or loss, thermoregulation, physical exercise, and psychiatric diseases. The various forms of thyroid allostasis pose serious problems in differential diagnosis of thyroid disease. This review article provides an overview of physiological mechanisms as well as major diagnostic and therapeutic implications of thyroid allostasis under a variety of developmental and straining conditions.