The role of cytokines in the lipopolysaccharide-induced sick euthyroid syndrome in mice

Prognostic role of euthyroid sick syndrome in MIS-C: results from a single-center observational study

Background

Euthyroid sick syndrome (ESS) is characterized by low serum levels of free triiodothyronine (fT3) with normal or low levels of thyroid stimulating hormone (TSH) and free thyroxine (fT4) and is reported in different acute clinical situations, such as sepsis, diabetic ketoacidosis and after cardiac surgery. Our aim was to evaluate the predicting role of ESS for disease severity in patients with Multisystem Inflammatory Syndrome in children (MIS-C).

Methods

A single-centre observational study on consecutive patients with MIS-C. Before treatment clinical, and laboratory data were collected and, in a subset of patients, thyroid function tests were repeated 4 weeks later. Variables distribution was analyzed by Mann-Whitney U-test and correlations between different parameters were calculated by Spearman's Rho coefficient.

Results

Forty-two patients were included and 36 (85.7%) presented ESS. fT3 values were significantly lower in patients requiring intensive care, a strong direct correlation was shown between fT3 and Hb, platelet count and ejection fraction values. A significant inverse correlation was retrieved between fT3 levels and C-reactive protein, brain natriuretic peptide, IL-2 soluble receptor and S-100 protein. Subjects with severe myocardial depression (EF < 45%) had lower fT3 values than subjects with higher EF. The thyroid function tests spontaneously normalized in all subjects who repeated measurement 4 weeks after admission.

Conclusion

ESS is a frequent and transient condition in acute phase of MIS-C. A severe reduction of fT3 must be considered as important prognostic factor for severe disease course, with subsequent relevant clinical impact in the management of these patients.

An update on non-thyroidal illness syndrome

The non-thyroidal illness syndrome (NTIS) was first reported in the 1970s as a remarkable ensemble of changes in serum TH (TH) concentrations occurring in probably any severe illness. Ever since, NTIS has remained an intriguing phenomenon not only because of the robustness of the decrease in serum triiodothyronine (T3), but also by its clear correlation with morbidity and mortality. In recent years, it has become clear that (parenteral) feeding in patients with critical illness should be taken into account as a major determinant not only of NTIS but also of clinical outcome. Moreover, both experimental animal and clinical studies have shown that tissue TH concentrations during NTIS do not necessarily reflect serum low TH concentrations and may decrease, remain unaltered, or even increase according to the organ and type of illness studied. These differential changes now have a solid basis in molecular studies on organ-specific TH transporters, receptors and deiodinases. Finally, the role of inflammatory pathways in these non-systemic changes has begun to be clarified. A fascinating role for TH metabolism in innate immune cells, including neutrophils and monocytes/macrophages, was reported in recent years, but there is no evidence at this early stage that this may be a determinant of susceptibility to infections. Although endocrinologists have been tempted to correct NTIS by TH supplementation, there is at present insufficient evidence that this is beneficial. Thus, there is a clear need for adequately powered randomized clinical trials (RCT) with clinically relevant endpoints to fill this knowledge gap.

Incidence of low-triiodothyronine syndrome in patients with septic shock

OBJECTIVE

Low levels of thyroid hormones have been associated with poor clinical outcomes. This metabolic situation, designated euthyroid sick syndrome, has been interpreted as a state of adaptation to different pathological processes, characterized by the decrease in plasma triiodothyronine. The present study seeks to determine the incidence of this disorder in patients with septic shock and its relationship with other severity indices and clinical outcomes.

METHODS

This prospective analytical study evaluated patients admitted to the intensive care unit with septic shock between April 2018 and July 2019. Variables associated with septic shock and thyroid profile were recorded at the time of the septic shock diagnosis and 7, 14, and 21 days later.

RESULTS

A total of 27 patients who met the inclusion criteria were analyzed. The incidence of an altered thyroid axis was 96.3%, with a mortality at 28 days of 36.7%. Patients without hormonal alteration did not present negative outcomes. Among those with low triiodothyronine, 42.3% recovered their thyroid function within 28 days, in whom mortality was 0%; 57.7% did not recover their thyroid function, in whom mortality was 66.7%. Those whose thyroid axis was altered and who did not normalize its function required more doses of vasoactives and had deteriorated lactate clearance.

CONCLUSION

Patients with septic shock have a high incidence of alteration of the thyroid axis, and this dysfunction is associated with higher mortality.

Thyroid Dysfunction and Nodular Goiter in Hemodialysis and Peritoneal Dialysis Patients

Objective

To investigate the prevalence of nodular goiter and thyroid dysfunction in uremic patients undergoing hemodialysis (HD) and peritoneal dialysis.

Design

Cross-sectional study.

Setting

Single dialysis unit and outpatient clinic.

Patients

The study included 221 patients [143 HD and 78 continuous ambulatory peritoneal dialysis (CAPD) patients] along with 135 consecutively selected outpatients as controls.

Main Outcome Measures

Ultrasonography was used to detect patients’ thyroid function and nodular goiter.

Results

Nodular goiter was detected in 54.8% of the uremic patients and in 21.5% of the controls. Uremic patients had higher prevalence of thyroid dysfunction, which included reduced serum concentration of total T3, total T4, and free T4, and increased serum level of TSH. Hypothyroidism was also observed more frequently in uremic patients than in the control group (5.4% vs 0.7%, p < 0.05). Nodular goiter was more frequently found in females than in males (63.5% vs 48%, p < 0.05). Moreover, the prevalence of nodular goiter increased with age (p < 0.02) in uremic patients. Hemodialysis patients had a higher frequency of reduced total T3 level (46.9% vs 29.5%, p < 0.02). However, CAPD patients had lower T4 levels (6.23 ± 1.82μg/dL vs 7.15± 1.99μg/dL, p < 0.05).

Conclusion

Because of the high incidence of hypothyroidism and nodular goiter in uremic patients, screening of thyroid function and goiter detection with ultrasound should be considered in evaluation of end-stage renal disease patients.

The role of IL-6 in exercise-induced anorexia in normal-weight boys

Our previous study showed that interleukin-6 (IL-6) is associated with suppression of appetite after high-intensity exercise (HIEX), but an independent role in food intake (FI) was not defined. We hypothesized that IL-6 suppresses appetite and FI, independently of appetite hormones, after HIEX in normal-weight (NW) boys. We investigated the effect of HIEX, with and without the inflammation inhibitor ibuprofen (IBU), on IL-6, other biomarkers of inflammation and appetite, FI, and ratings of appetite in NW boys. Fifteen NW boys (aged 13–18 years) were randomly assigned in a crossover design to 4 sessions: (i) water and rest, (ii) IBU and rest, (iii) water and HIEX, and (iv) IBU and HIEX. HIEX consisted of three 10-min bouts of exercise at 75% of maximal oxygen uptake with 90 s of active rest between bouts. IBU (300 mg) was given as a liquid suspension. FI, ratings of appetite, and plasma biomarkers of appetite, inflammation, stress, and glucose control were measured. FI was not affected by HIEX or IBU. Appetite increased over time (p = 0.002) but was lower after HIEX (p < 0.001) and not affected by IBU. HIEX, but not IBU, resulted in higher levels of IL-6 (p < 0.001) and cortisol (p < 0.001) and lower active ghrelin (p < 0.001). IL-6 correlated with active ghrelin (r = 0.37; p = 0.036) and cortisol (r = 0.26; p = 0.049). An independent role for IL-6 in appetite suppression was not supported. However, IL-6 was correlated with active ghrelin and cortisol, thus potentially mediating appetite via these interactions.

Expression levels of interferon-ɣ and type 2 deiodinase in patients diagnosed with recurrent depressive disorders

BACKGROUND

Thyroid hormones (TH) are involved in modulation of the immune system and inflammation. TH dysregulation is associated with depressive disorders. The iodothyronine deiodinases (DIOs), the key enzymes for TH synthesis, can be affected and induced by pro-inflammatory cytokines. We aimed to investigate the levels of and correlation between type 2 DIO (DIO2) and interferon-gamma (IFN-ɣ) in patients with recurrent depressive disorders (rDD).

METHODS

Data from 91 rDD patients and 105 healthy controls were analyzed. The diagnoses are based on the ICD-10 criteria (F33.0-F33.8). Expression levels of DIO2 and IFN-ɣ were estimated using the method based on the polymerase chain reaction and the enzyme-linked immunosorbent assay (ELISA).

RESULTS

The DIO2 expression on mRNA/protein levels in rDD patients (both female and males) was reduced as compared with the control subjects. No correlation between DIO2 and IFN-ɣ expression was observed.

CONCLUSION

This is the first study to reveal that one may cautiously suggest that DIO2 may be involved in the development and/or progression of rDD. The mechanisms of TH regulation on depression, however, need further investigation.

The classic pathways of thyroid hormone metabolism

Thyroid hormones (TH) are crucial for growth and development and play an important role in energy homeostasis. Although serum TH levels are relatively constant in the physiological state, TH bioavailability at the tissue and cellular level is dependent on local TH metabolism. Circulating TH produced by the thyroid can be metabolized by a number of different pathways resulting in 1) activation of TH 2) deactivation of TH or 3) excretion of TH and subsequent metabolites. These pathways play an essential role in determining local TH levels and action. The major classical pathways of TH metabolism are deiodination, sulfation, glucuronidation, and ether-link cleavage. This review provides an overview of these pathways, their relative contributions to TH levels in the serum and in various organs and the changes in these pathways elicited by fasting and illness.

Decreased Appetite after High-Intensity Exercise Correlates with Increased Plasma Interleukin-6 in Normal-Weight and Overweight/Obese Boys

Background: High-intensity exercise (HIEX) suppresses appetite in adults and is thought to be mediated by appetite-regulating hormones. However, the effects of HIEX-induced inflammatory and stress biomarkers on appetite control and body weight have not been reported in children or adults. Objective: The objective of this study was to describe the effects of acute HIEX at 70% peak oxygen consumption (VO2peak) on postexercise appetite and selective biomarkers of inflammation, stress, and appetite regulatory hormones in normal-weight (NW) and in overweight/obese boys. Methods: NW (n = 11) and overweight/obese (n = 11) boys aged 10-18 y were randomly assigned in a crossover design to either rest or HIEX. Visual analog scale appetite ratings and plasma biomarkers of appetite, inflammation, stress, and glucose control were measured after HIEX or rest. Results: Appetite increased from baseline to 110 min (P < 0.001), but was lower after HIEX (P = 0.04), with no difference between body weight groups. HIEX also resulted in lower active ghrelin (P < 0.001) and increased interleukin-6 (IL-6; P < 0.001), tumor necrosis factor-α (P < 0.001), and cortisol (P < 0.001) concentrations, independent of body weight. It increased blood glucose (P = 0.002) and insulin (P = 0.028) concentrations in NW but not overweight and obese boys. Leptin, glucagon-like peptide 1, peptide tyrosine tyrosine, C-reactive protein, and cortisol were not affected by HIEX. An inverse correlation was found between IL-6 and appetite (r = -0.379; P = 0.012), but not any other biomarkers. Conclusions: HIEX resulted in reduced appetite that correlated with an increase in IL-6 in both NW and overweight/obese boys. However, although a role for IL-6 in the response can be suggested, the suppression of appetite was potentially mediated by the decrease in active ghrelin and/or increase in cortisol. This trial was registered at clinicaltrials.gov as NCT02619461.

Thyroid Hormone in the Pediatric Intensive Care Unit

Thyroid hormones are key factors necessary for normal growth and development in children. They have tight control of metabolic rate and, as a result, frequently become altered in their synthesis and/or release during times of stress or critical illness. Disturbances in thyroid hormone homeostasis have been well described in several pathologic states, including sepsis/septic shock, renal failure, trauma, severe malnutrition, and following cardiopulmonary bypass. Specifically, a decrease in serum triiodothyronine (T₃) and a concomitant increase in reverse triiodothyronine (rT₃) levels are the most common changes observed. It is further noteworthy that serum thyroxine (T₄), rT₃, and T₃ levels change in relation to severity of nonthyroidal illness. Many past investigators have speculated that these alterations are a teleological adaptation to severe illness and the increased metabolic demands that critical illness bears. However, this paradigm has been challenged through multiple avenues and has lost support over the past few years. Instead the "inflammatory hypothesis" has emerged implicating a cytokine surge as the mediator of thyroid hormone disruption. Overall, the demonstrated association between low thyroid hormone levels and poor clinical outcomes, the beneficial effects of thyroid hormone supplementation in multiple critically ill subpopulations, and the well-established safety profile of T₃ therapy make thyroid hormone supplementation in the pediatric ICU worth consideration.

Environmental heat stress modulates thyroid status and its response to repeated endotoxin challenge in steers

The objective of this study was to evaluate in cattle, the effects of acute exposure to a heat stress (HS) environment on the status of the pituitary (thyrotropin, TSH)-thyroid (thyroxine, T4)-peripheral tissue T4 deiodination (type 1 5'-deiodinase [D1]; triiodothyronine [T3]; reverse-triiodothyronine [rT3]) axis, and the further response of this pituitary-thyroid-peripheral tissue axis (PTTA) to perturbation caused by the induction of the proinflammatory innate immune state provoked by the administration of gram-negative bacteria endotoxin (lipopolysaccharide [LPS]). Ten steers (318 ± 49 kg body weight) housed in controlled environment chambers were subjected to either a thermoneutral (TN: constant 19°C) or HS temperature conditions (cyclical daily temperatures: 32.2°C-40.0°C) for a total period of 9 d. To minimize the effects of altered plane of nutrition due to HS, steers in TN were pair-fed to animals in HS conditions. Steers received 2 LPS challenges 3 d apart (LPS1 and LPS2; 0.2 μg/kg body weight, intravenously, Escherichia coli 055:B5) with the first challenge administered on day 4 relative to the start of the environmental conditioning. Jugular blood samples were collected at 0, 1, 2, 4, 7, and 24 h relative to the start of each LPS challenge. Plasma TSH, T4, T3, and rT3 were measured by radioimmunoassay. Liver D1 activity was measured in biopsy samples collected before the LPS1 (0 h) and 24 h after LPS2. Before the start of LPS1, HS decreased (P < 0.01 vs TN) plasma TSH (40%), T4 (45.4%), and T3 (25.9%), but did not affect rT3 concentrations. In TN steers, the LPS1 challenge decreased (P < 0.01 vs 0 h) plasma concentrations of TSH between 1 and 7 h and T4 and T3 at 7 and 24 h. In HS steers, plasma TSH concentrations were decreased at 2 h only (P < 0.05), whereas plasma T3 was decreased at 7 and 24 h (P < 0.01). Whereas plasma T4 concentrations were already depressed in HS steers at 0 h, LPS1 did not further affect the levels. Plasma rT3 concentrations were increased in all steers at 4, 7, and 24 h after LPS1 (P < 0.01). The patterns of concentration change of T4, T3, and rT3 during LPS2 mirrored those observed in LPS1; the responses in plasma TSH were of smaller magnitude than those incurred after LPS1. The LPS challenges reduced (P < 0.01) hepatic activity of D1 in all animals but no differences were observed between steers subjected to TN or HS environment. The data are consistent with the concept that acute exposure of cattle to a HS environment results in the depression of the pituitary and thyroid components of the PTTA, whereas a normal capacity to generate T3 from T4 in the liver is preserved. The data also suggest that LPS challenge further suppresses all components of the PTTA including liver T3 generation, and these PTTA perturbations are more pronounced in steers that encounter a HS exposure.

The molecular basis of the non-thyroidal illness syndrome

The 'sick euthyroid syndrome' or 'non-thyroidal illness syndrome' (NTIS) occurs in a large proportion of hospitalized patients and comprises a variety of alterations in the hypothalamus-pituitary-thyroid (HPT) axis that are observed during illness. One of the hallmarks of NTIS is decreased thyroid hormone (TH) serum concentrations, often viewed as an adaptive mechanism to save energy. Downregulation of hypophysiotropic TRH neurons in the paraventricular nucleus of the hypothalamus and of TSH production in the pituitary gland points to disturbed negative feedback regulation during illness. In addition to these alterations in the central component of the HPT axis, changes in TH metabolism occur in a variety of TH target tissues during NTIS, dependent on the timing, nature and severity of the illness. Cytokines, released during illness, are known to affect a variety of genes involved in TH metabolism and are therefore considered a major determinant of NTIS. The availability of in vivo and in vitro models for NTIS has elucidated part of the mechanisms involved in the sometimes paradoxical changes in the HPT axis and TH responsive tissues. However, the pathogenesis of NTIS is still incompletely understood. This review focusses on the molecular mechanisms involved in the tissue changes in TH metabolism and discusses the gaps that still require further research.

Hypothalamic-pituitary hormones during critical illness: a dynamic neuroendocrine response

Independent of the underlying condition, critical illness is characterized by a uniform dysregulation of the hypothalamic-pituitary-peripheral axes. In most axes a clear biphasic pattern can be distinguished. The acute phase of critical illness is characterized by low peripheral effector hormone levels such as T3, IGF-1 and testosterone, despite an actively secreting pituitary. The adrenal axis with high cortisol levels in the presence of low ACTH levels is a noteworthy exception. In the prolonged phase of critical illness, low peripheral effector hormone levels coincide with a uniform suppression of the neuroendocrine axes, predominantly of hypothalamic origin. The severity of the alterations in the different neuroendocrine axes is associated with a high risk of morbidity and mortality, but it remains unknown whether the observed changes are cause or consequence of adverse outcome. Several studies have identified therapeutic potential of hypothalamic releasing factors, but clinical outcome remains to be investigated with sufficiently powered randomized controlled trials.

American Thyroid Association Guide to investigating thyroid hormone economy and action in rodent and cell models

BACKGROUND

An in-depth understanding of the fundamental principles that regulate thyroid hormone homeostasis is critical for the development of new diagnostic and treatment approaches for patients with thyroid disease.

SUMMARY

Important clinical practices in use today for the treatment of patients with hypothyroidism, hyperthyroidism, or thyroid cancer are the result of laboratory discoveries made by scientists investigating the most basic aspects of thyroid structure and molecular biology. In this document, a panel of experts commissioned by the American Thyroid Association makes a series of recommendations related to the study of thyroid hormone economy and action. These recommendations are intended to promote standardization of study design, which should in turn increase the comparability and reproducibility of experimental findings.

CONCLUSIONS

It is expected that adherence to these recommendations by investigators in the field will facilitate progress towards a better understanding of the thyroid gland and thyroid hormone dependent processes.

The renin-angiotensin system in thyroid disorders and its role in cardiovascular and renal manifestations

Thyroid disorders are among the most common endocrine diseases and affect virtually all physiological systems, with an especially marked impact on cardiovascular and renal systems. This review summarizes the effects of thyroid hormones on the renin-angiotensin system (RAS) and the participation of the RAS in the cardiovascular and renal manifestations of thyroid disorders. Thyroid hormones are important regulators of cardiac and renal mass, vascular function, renal sodium handling, and consequently blood pressure (BP). The RAS acts globally to control cardiovascular and renal functions, while RAS components act systemically and locally in individual organs. Various authors have implicated the systemic and local RAS in the mediation of functional and structural changes in cardiovascular and renal tissues due to abnormal thyroid hormone levels. This review analyzes the influence of thyroid hormones on RAS components and discusses the role of the RAS in BP, cardiac mass, vascular function, and renal abnormalities in thyroid disorders.

Contribution of nutritional deficit to the pathogenesis of the nonthyroidal illness syndrome in critical illness: a rabbit model study

Both starvation and critical illness are hallmarked by changes in circulating thyroid hormone parameters with typically low T(3) concentrations in the absence of elevated TSH. This constellation is labeled nonthyroidal illness (NTI). Because critical illness is often accompanied by anorexia and a failing gastrointestinal tract, the NTI of critical illness may be confounded by nutrient deficiency. In an experimental study performed in a rabbit model, we investigated the impact of nutritional deficit on the NTI of sustained critical illness. Critically ill rabbits were randomly allocated to parenteral nutrition (moderate dose 270 kcal/d) initiated on the day after injury and continued until d 7 of illness or to infusing a similar volume of dextrose 1.4% (14 kcal/d). With early parenteral nutrition during illness, the decrease in serum T(3) observed with fasting was reversed, whereas the fall in T(4) was not significantly affected. The rise in T(3) with parenteral nutrition paralleled an increase of liver and kidney type-1 and a decrease of liver and kidney type-3 deiodinase activity and an increase in circulating and central leptin. Nuclear staining of constitutive androstane receptor and its downstream expression of sulfotransferases were reduced in fasting ill animals. TRH expression in the hypothalamus was not different in fasted and fed ill rabbits, although circulating TSH levels were higher with feeding. In conclusion, in this rabbit model of sustained critical illness, reduced circulating T(3), but not T(4), levels could be prevented by parenteral nutrition, which may be mediated by leptin and its actions on tissue deiodinase activity.

Role of type 2 deiodinase in response to acute lung injury (ALI) in mice

Thyroid hormone (TH) metabolism, mediated by deiodinase types 1, 2, and 3 (D1, D2, and D3) is profoundly affected by acute illness. We examined the role of TH metabolism during ventilator-induced lung injury (VILI) in mice. Mice exposed to VILI recapitulated the serum TH findings of acute illness, namely a decrease in 3,5,3'-triiodothyronine (T(3)) and thyroid-stimulating hormone and an increase in reverse T(3). Both D2 immunoreactivity and D2 enzymatic activity were increased significantly. D1 and D3 activity did not change. Using D2 knockout (D2KO) mice, we determined whether the increase in D2 was an adaptive response. Although similar changes in serum TH levels were observed in D2KO and WT mice, D2KO mice exhibited greater susceptibility to VILI than WT mice, as evidenced by poorer alveoli integrity and quantified by lung chemokine and cytokine mRNA induction. These data suggest that an increase in lung D2 is protective against VILI. Similar findings of increased inflammatory markers were found in hypothyroid WT mice exposed to VILI compared with euthyroid mice, indicating that the lungs were functionally hypothyroid. Treatment of D2KO mice with T(3) reversed many of the lung chemokine and cytokine profiles seen in response to VILI, demonstrating a role for T(3) in the treatment of lung injury. We conclude that TH metabolism in the lung is linked to the response to inflammatory injury and speculate that D2 exerts its protective effect by making more TH available to the injured lung tissue.

Beyond low plasma T3: local thyroid hormone metabolism during inflammation and infection

Decreased serum thyroid hormone concentrations in severely ill patients were first reported in the 1970s, but the functional meaning of the observed changes in thyroid hormone levels, together known as nonthyroidal illness syndrome (NTIS), remains enigmatic. Although the common view was that NTIS results in overall down-regulation of metabolism in order to save energy, recent work has shown a more complex picture. NTIS comprises marked variation in transcriptional and translational activity of genes involved in thyroid hormone metabolism, ranging from inhibition to activation, dependent on the organ or tissue studied. Illness-induced changes in each of these organs appear to be very different during acute or chronic inflammation, adding an additional level of complexity. Organ- and timing-specific changes in the activity of thyroid hormone deiodinating enzymes (deiodinase types 1, 2, and 3) highlight deiodinases as proactive players in the response to illness, whereas the granulocyte is a novel and potentially important cell type involved in NTIS during bacterial infection. Although acute NTIS can be seen as an adaptive response to support the immune response, NTIS may turn disadvantageous when critical illness enters a chronic phase necessitating prolonged life support. For instance, changes in thyroid hormone metabolism in muscle during critical illness may be relevant for the pathogenesis of myopathy associated with prolonged ventilator dependence. This review focuses on NTIS as a timing-related and organ-specific response to illness, occurring independently from the decrease in serum thyroid hormone levels and potentially relevant for disease progression.

Acute inflammation increases pituitary and hypothalamic glycoprotein hormone subunit B5 mRNA expression in association with decreased thyrotrophin receptor mRNA expression in mice

The biological function of thyrostimulin, consisting of the GPA2 and GPB5 subunit, is currently poorly understood. The recent observation that pro-inflammatory cytokines up-regulate the transcription of GPB5 in vitro suggested a role for thyrostimulin in the nonthyroidal illness syndrome, a state of altered thyroid hormone metabolism occurring during illness. In the present study, we used GPB5 knockout (GPB5(-/-) ) and wild-type (WT) mice to evaluate the role of GPB5 in the pituitary and hypothalamus during acute inflammation induced by lipopolysaccharide (LPS, bacterial endotoxin) administration. We evaluated serum thyroid hormones and mRNA expression of genes involved in thyroid hormone metabolism in the pituitary and in two hypothalamic regions; the periventricular region (PE) and the arcuate nucleus/median eminence region. As expected, LPS administration increased deiodinase type 2 mRNA in the PE, at the same time as decreasing pituitary thyrotrophin (TSH)β mRNA and serum thyroxine and triiodothyronine both in GPB5(-/-) and WT mice. GPB5 mRNA, but not GPA2 mRNA, markedly increased after LPS in the pituitary (200-fold) and hypothalamus of WT mice. In addition, we found large (>50%) suppression of TSH receptor (TSHR) mRNA in the pituitary and hypothalamus of WT mice but not in GPB5(-/-) mice. In conclusion, our results demonstrate in vivo regulation of central GPB5 transcription during acute illness. The observed differences between GPB5(-/-) and WT mice point to a distinct role for GPB5 in pituitary and hypothalamic TSHR suppression during acute illness.

The nonthyroidal illness syndrome in the non-critically ill patient

BACKGROUND

The nonthyroidal illness syndrome (NTIS) is a very common clinical entity among hospitalized patients and has been reported in practically every severe illness and acute or chronic stressful event. There is a large body of data associating the presence of NTIS with the severity of the underlying disease. Most of these studies concern intensive care unit (ICU) patients, whereas the non-critically ill patients outside the ICU setting are less well studied.

DESIGN

We provide a review of the existing literature focusing on studies examining NTIS in non-critically ill patients and attempt to summarize the pathophysiological pathways underlying the syndrome, its prognostic role, as well as the current intervention studies mainly from a clinical standpoint.

RESULTS

The aetiology of the NTIS is multifactorial and varies among different groups of patients. Experimental and clinical findings suggest that inflammatory cytokines are implicated in the pathogenesis of the syndrome, whereas recent evidence re-evaluate the role of deiodinases in thyroid hormone metabolism not only in the periphery but also in the hypothalamus and the pituitary and thus in the alterations accompanying NTIS. Clinical data examining the effectiveness of thyroid hormone supplementation in NTIS remain controversial.

CONCLUSIONS

As long as there is no clear evidence of benefit from thyroid hormone replacement and until well-designed studies confirm its efficacy, thyroxine supplementation should not be recommended for the treatment of NTIS.

NF-kappaB p65 subunit mediates lipopolysaccharide-induced Na(+)/I(-) symporter gene expression by involving functional interaction with the paired domain transcription factor Pax8

The Gram-negative bacterial endotoxin lipopolysaccharide (LPS) elicits a variety of biological responses. Na(+)/I(-) symporter (NIS)-mediated iodide uptake is the main rate-limiting step in thyroid hormonogenesis. We have recently reported that LPS stimulates TSH-induced iodide uptake. Here, we further analyzed the molecular mechanism involved in the LPS-induced NIS expression in Fisher rat thyroid cell line 5 (FRTL-5) thyroid cells. We observed an increase in TSH-induced NIS mRNA expression in a dose-dependent manner upon LPS treatment. LPS enhanced the TSH-stimulated NIS promoter activity denoting the NIS-upstream enhancer region (NUE) as responsible for the stimulatory effects. We characterized a novel putative conserved kappaB site for the transcription factor nuclear factor-kappaB (NF-kappaB) within the NUE region. NUE contains two binding sites for the transcription factor paired box 8 (Pax8), main regulator of NIS transcription. A physical interaction was observed between the NF-kappaB p65 subunit and paired box 8 (Pax8), which appears to be responsible for the synergic effect displayed by these transcription factors on NIS gene transcription. Moreover, functional blockage of NF-kappaB signaling and site-directed mutagenesis of the kappaB cis-acting element abrogated LPS stimulation. Silencing expression of p65 confirmed its participation as an effector of LPS-induced NIS stimulation. Furthermore, chromatin immunoprecipitation corroborated that NIS is a novel target gene for p65 transactivation in response to LPS. Moreover, we were able to corroborate the LPS-stimulatory effect on thyroid cells in vivo in LPS-treated rats, supporting that thyrocytes are capable of responding to systemic infections. In conclusion, our results reveal a new mechanism involving p65 in the LPS-induced NIS expression, denoting a novel aspect in thyroid cell differentiation.

Endotoxin, zymosan, and cytokines decrease the expression of the transcription factor, carbohydrate response element binding protein, and its target genes

Carbohydrate response element binding protein (ChREBP) is a recently discovered transcription factor whose levels and activity are increased by glucose leading to the activation of target genes, which include acetyl-CoA carboxylase, fatty acid synthase, and liver-type pyruvate kinase. Here, we demonstrate that lipopolysaccharide (LPS) treatment causes a marked decrease in ChREBP mRNA and protein levels in the liver of mice fed a normal chow diet or in mice fasted for 24 h and then re-fed a high carbohydrate diet. This decrease occurs rapidly and is a sensitive response (half-maximal dose 0.1 μg/mouse). The decrease in ChREBP is accompanied by a decrease in the expression of ChREBP target genes. Zymosan and turpentine treatment also decrease hepatic ChREBP levels and the expression of its target genes. Additionally, tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1β) decrease liver ChREBP expression both in vivo and in Hep3B cells in culture. Finally, LPS decreased ChREBP expression in muscle and adipose tissue. These studies demonstrate that ChREBP is down-regulated during the acute phase response resulting in alterations in the expression of ChREBP regulated target genes. Thus, ChREBP joins a growing list of transcription factors that are regulated during the acute phase response.

Nonthyroidal illness syndrome in children

Neuroendocrine changes in the hypothalamic-pituitary-thyroid axis during critical illness result in nonthyroidal illness syndrome (NTIS) characterized by abnormal thyrotropin (TSH) and thyroid hormone levels. Studies looking at the natural history of neuroendocrine changes during critical illness have revealed the presence of NTIS. NTIS has been described in a variety of patient settings. Many studies have tried to uncover the pathophysiology behind NTIS and several theories are proposed. Whether NTIS requires treatment or intervention is still controversial and the results of the treatment studies are arguably mixed. Whether implicitly stated or not, the underlying purpose of all the natural history, pathophysiology, or treatment studies is to determine whether NTIS is adaptive or maladaptive. Some studies have illustrated a correlation between illness severity and the degree of NTIS but a cause and effect relationship is still elusive. The human studies can be divided between those with either adult or pediatric subjects, with much less data available in the latter. This review examines the available literature on NTIS with an emphasis on the pediatric literature.

Selenium and thyroid hormone axis in critical ill states: an overview of conflicting view points

In critical ill states the plasma selenium levels are low and inversely correlated with the severity and outcome of the disease. The plasma selenium levels indicate the amount of circulating selenoproteins and selenoenzymes. These are important for the maintenance of the redox system, modulating the immune system and also for thyroid hormone metabolism. Not only all three deiodinases (D1-3) are selenoenzymes, but within the thyroid gland there are several other selenoenzymes, which are important for the maintenance of normal thyroid function. In critical ill states also triodothyronine (T3) is low and reverse T3 elevated, and also TSH and thyroxin (T4) are low, correlating like low plasma selenium with the severity of the disease. Subsequently, several intervention trials had been performed to evaluate whether an adjuvant selenium supplementation might attenuate the course of the disease and improve outcome. The selenium supplementation improved outcome and even reduced mortality in some but not all prospective randomized trials. A few prospective randomized intervention trials with selenium supplementation had also been performed to evaluate the hypothesis, whether low selenium is the cause of low-T3-syndrome, however, with conflicting results and no clear evidence that low D1 activity is due to the selenium deficiency in critical illness. Because D1 catalyses the conversion of T4 to T3 and also the clearance of reverse T3, low D1 activity would sufficiently explain low plasma T3 and elevated reverse T3. It had been, however, clearly shown that cytokines are responsible for the inhibition of D1 activity, but D2 and D3 are even higher during acute inflammation in critically ill patients. One of the most important effects of selenium on the immune system seems to be the reduction of cytokine release and therefore an indirect connection between low selenium and low D1 activity has to be postulated and not a lower D1 activity due to lower availability of selenium for the D1 expression.

Cellular and molecular basis of deiodinase-regulated thyroid hormone signaling

The iodothyronine deiodinases initiate or terminate thyroid hormone action and therefore are critical for the biological effects mediated by thyroid hormone. Over the years, research has focused on their role in preserving serum levels of the biologically active molecule T(3) during iodine deficiency. More recently, a fascinating new role of these enzymes has been unveiled. The activating deiodinase (D2) and the inactivating deiodinase (D3) can locally increase or decrease thyroid hormone signaling in a tissue- and temporal-specific fashion, independent of changes in thyroid hormone serum concentrations. This mechanism is particularly relevant because deiodinase expression can be modulated by a wide variety of endogenous signaling molecules such as sonic hedgehog, nuclear factor-kappaB, growth factors, bile acids, hypoxia-inducible factor-1alpha, as well as a growing number of xenobiotic substances. In light of these findings, it seems clear that deiodinases play a much broader role than once thought, with great ramifications for the control of thyroid hormone signaling during vertebrate development and metamorphosis, as well as injury response, tissue repair, hypothalamic function, and energy homeostasis in adults.

Regulation of tissue iodothyronine deiodinase activity in a model of prolonged critical illness

BACKGROUND

The low plasma triiodothyronine (T3) observed during prolonged critical illness can be explained in part by suppressed hepatic deiodinase type I (D1) and increased D3 activity. Infusion of thyrotropin-releasing hormone (TRH) can restore D1 and D3 activity in critically ill rabbits, but it remains unknown whether this is a direct effect of TRH or the TRH-induced rise in circulating thyroxine (T4) and T3.

METHODS

To answer this specific question, burn-injured rabbits randomly received a 4-day treatment with saline, T4, T3, T4+T3, or TRH, started on day 4 of the illness. Plasma iodothyronine concentrations, D1 and D3 activity, and T3-responsive gene expression were quantified in liver and kidney.

RESULTS

Infusion of T4, T3, or TRH increased circulating T3 levels and hepatic D1 activity. Co-infusion of T3 with T4 enhanced T4 to T3 conversion as demonstrated by lower T4, higher T3, and lower reverse T3 (rT3) levels and tended to further increase hepatic D1 activity. Hepatic D1 activity correlated positively with circulating T3 and the T3/rT3 ratio, but not with T4, rT3, or thyroid-stimulating hormone.

CONCLUSIONS

During prolonged critical illness, D1 activity is primarily regulated via changes in circulating T3, suggesting that the low plasma T3 concentrations may be important in sustaining low D1 activity in this condition.

Identification of molecular mechanisms related to nonthyroidal illness syndrome in skeletal muscle and adipose tissue from patients with septic shock

OBJECTIVE

Septic shock is one of various causes of nonthyroidal illness syndrome (NTIS). In humans, the molecular mechanisms involved in NTIS are mostly unknown. The aim of this study was to investigate, in patients with NTIS secondary to septic shock, changes in the expression of genes involved in the actions of thyroid hormones and in the activity of deiodinase enzymes, in two tissues important for protein and energy metabolism, skeletal muscle (SM) and subcutaneous adipose tissue (SAT).

DESIGN

Hospitalized patients were divided into a control and a septic shock NTIS group.

MEASUREMENT

Serum collection for biochemical measurements, and SM and SAT biopsies for mRNA expression analysis of thyroid hormone receptors (THRB1, THRA1), retinoid X receptors (RXRA, RXRB, RXRG), nuclear receptor corepressor (NCOR1), silencing mediator of retinoid and thyroid hormone receptor (SMRT), steroid receptor coactivator (SRC1), type 1 and 2 deiodinases (D1, D2), monocarboxylate transporter 8 (MCT8), SECIS binding protein 2 (SBP2) and uncoupling protein 3 (UCP3) as well as D1, D2 and D3 enzyme activity measurements.

RESULTS

The NTIS group had lower serum TSH, and free T3 and higher rT3 than controls. D1 and D3 were detected in SAT, with no differences found between the two groups; SM had very low D2 activity and again no differences were found between groups; D3 activity in SM was higher in NTIS than controls. SM expression of THRB1, RXRG and D2 was lower and RXRA higher in NTIS than controls. SAT from NTIS patients had lower MCT8, THRB1, THRA1, RXRG and SMRT, and higher UCP3 expression than controls.

CONCLUSIONS

In patients with septic shock NTIS tissue responses are orientated to decrease production and increase degradation (muscle) or decrease uptake (adipose tissue) of T3, as well as to decrease thyroid hormone actions.

Relating circulating thyroid hormone concentrations to serum interleukins-6 and -10 in association with non-thyroidal illnesses including chronic renal insufficiency

BACKGROUND

Because of the possible role of cytokines including interleukins (IL) in systemic non-thyroidal illnesses' (NTI) pathogenesis and consequently the frequently associated alterations in thyroid hormone (TH) concentrations constituting the euthyroid sick syndrome (ESS), we aimed in this research to elucidate the possible relation between IL-6 & IL-10 and any documented ESS in a cohort of patients with NTI.

METHODS

Sixty patients and twenty healthy volunteers were recruited. The patients were subdivided into three subgroups depending on their underlying NTI and included 20 patients with chronic renal insufficiency (CRI), congestive heart failure (CHF), and ICU patients with myocardial infarction (MI). Determination of the circulating serum levels of IL-6 and IL-10, thyroid stimulating hormone (TSH), as well as total T4 and T3 was carried out.

RESULTS

In the whole group of patients, we detected a significantly lower T3 and T4 levels compared to control subjects (0.938 +/- 0.477 vs 1.345 +/- 0.44 nmol/L, p = 0.001 and 47.9 +/- 28.41 vs 108 +/- 19.49 nmol/L, p < 0.0001 respectively) while the TSH level was normal (1.08+0.518 muIU/L). Further, IL-6 was substantially higher above controls' levels (105.18 +/- 72.01 vs 3.35 +/- 1.18 ng/L, p < 0.00001) and correlated negatively with both T3 and T4 (r = -0.620, p < 0.0001 & -0.267, p < 0.001, respectively). Similarly was IL-10 level (74.13 +/- 52.99 vs 2.64 +/- 0.92 ng/ml, p < 0.00001) that correlated negatively with T3 (r = -0.512, p < 0.0001) but not T4. Interestingly, both interleukins correlated positively (r = 0.770, p = <0.001). Moreover, IL-6 (R2 = 0.338, p = 0.001) and not IL-10 was a predictor of low T3 levels with only a borderline significance for T4 (R2 = 0.082, p = 0.071).By subgroup analysis, the proportion of patients with subnormal T3, T4, and TSH levels was highest in the MI patients (70%, 70%, and 72%, respectively) who displayed the greatest IL-6 and IL-10 concentrations (192.5 +/- 45.1 ng/L & 122.95 +/- 46.1 ng/L, respectively) compared with CHF (82.95 +/- 28.9 ng/L & 69.05 +/- 44.0 ng/L, respectively) and CRI patients (40.05 +/- 28.9 ng/L & 30.4 +/- 10.6 ng/L, respectively). Surprisingly, CRI patients showed the least disturbance in IL-6 and IL-10 despite the lower levels of T3, T4, and TSH in a higher proportion of them compared to CHF patients (40%, 45%, & 26% vs 35%, 25%, & 18%, respectively).

CONCLUSION

the high prevalence of ESS we detected in NTI including CRI may be linked to IL-6 and IL-10 alterations. Further, perturbation of IL-6 and not IL-10 might be involved in ESS pathogenesis although it is not the only key player as suggested by our findings in CRI.

Toll-like receptor-MyD88 and Fc receptor pathways of mast cells mediate the thyroid dysfunctions observed during nonthyroidal illness

Bacterial infections and other pathologic conditions induce complex dysfunctions of the hypothalamic-pituitary-thyroid axis, collectively known as nonthyroidal illness (NTI). To explore the pathogenesis of bacterial NTI, we injected Mycobacterium tuberculosis extracts or Escherichia coli LPS in mice lacking key components of the Toll-like receptor or crystallizable fragment (Fc) receptor pathways. In wild-type mice, the bacterial components induced a hypothyroidism characterized by elements of both hypothalamic and thyroidal dysfunction. This NTI hypothyroidism did not develop in mice lacking the MyD88 adaptor or in those with a reduced number of mast cells. The hypothyroid responsiveness to LPS, however, was restored upon reconstitution with mast cells derived from the bone marrow of wild-type donors. In addition to bacterial components, whole immunoglobulins induced NTI hypothyroidism in wild-type mice, but not in those lacking activating Fc receptors or mast cells. The study demonstrates a link between Toll-like and Fc receptor signaling and thyroid gland function, uncovering a role of mast cells in murine NTI.

The dynamic neuroendocrine response to critical illness

The severity of striking alterations in the hypothalamic-anterior pituitary-peripheral hormone axes, which are the hallmark of severity of critical illness, is associated with a high risk for morbidity and mortality. Most attempts to correct the hormone balance are ineffective or harmful because of lack of pathophysiologic understanding. Extensive research has provided more insight in the biphasic neuroendocrine response to critical illness: the acute phase is characterized by an actively secreting pituitary but low peripheral effector hormone levels. In contrast, in prolonged critical illness, uniform suppression of the neuroendocrine axes, predominantly of hypothalamic origin, contributes to low serum levels of the respective target-organ hormones.

Changes within the thyroid axis during the course of critical illness

This article reviews the mechanisms behind the observed changes in plasma thyroid hormone levels in the acute phase and the prolonged phase of critical illness. It focuses on the neuroendocrinology of the low triiodothyronine syndrome and on thyroid hormone metabolism by deiodination and transport.

Changes within the thyroid axis during critical illness

Pronounced alterations in plasma thyroid stimulating hormone and thyroid hormone levels occur during critical illness without any evidence for thyroid disease. Plasma T3 decreases and plasma rT3 increases within a few hours after the onset of disease, and the magnitude of these changes is related to the severity and the duration of the disease. This article reviews the mechanisms behind the observed changes, and focuses on the regulation of thyroid hormone deiodination and transport, as well as the potential positive or negative effects for both the acute and the chronic phase of critical illness.

Sick euthyroid syndrome is associated with decreased TR expression and DNA binding in mouse liver

Infection is associated with low serum thyroid hormones and thyrotropin levels. Here we demonstrate that infection also reduces thyroid hormone receptor (TR) expression. In gel shift experiments, retinoid X receptor (RXR)/TR DNA binding was reduced in mouse liver by 60 and 77%, respectively, 4 and 16 h after lipopolysaccharide (LPS) administration. Surprisingly, LPS did not decrease either TR-alpha or TR-beta protein levels at 4 h, but by 16 h TR-alpha(1), TR-alpha(2), and TR-beta levels were reduced by 55, 87, and 41%, respectively. We previously reported that LPS rapidly decreases RXR protein levels in liver. Therefore, we added RXR-beta to hepatic nuclear extracts prepared 4 h after LPS treatment, which restored RXR/TR DNA binding to a level comparable to that of controls. A similar experiment conducted on extracts prepared 16 h after LPS administration did not restore RXR/TR DNA binding. We propose that decreased RXR expression is limiting for RXR/TR DNA binding at 4 h, whereas the reduction in both TR and RXR levels results in further decreased binding at 16 h.

Characterization of mice deficient in the Src family nonreceptor tyrosine kinase Frk/rak

Frk/rak belongs to a novel family of Src kinases with epithelial tissue-specific expression. Although developmental expression patterns and functional overexpression in vitro have associated these kinases with growth suppression and differentiation, their physiological functions remain largely unknown. We therefore generated mice carrying a null mutation in iyk, the mouse homolog of Frk/rak. We report here that frk/rak(-/-) mice are viable, show similar growth rates to wild-type animals, and are fertile. Furthermore, a 2-year study of health and survival did not identify differences in the incidence and spectrum of spontaneous tumors or provide evidence of hyperplasias in frk/rak(-/-) epithelial tissues. Histological analysis of organs failed to reveal any morphological changes in epithelial tissues that normally express high levels of Frk/rak. Ultrastructural analysis of intestinal enterocytes did not identify defects in brush border morphology or structural polarization, demonstrating that Frk/rak is dispensable for intestinal cytodifferentiation. Additionally, frk/rak-null mice do not display altered sensitivity to intestinal damage induced by ionizing radiation. cDNA microarray analysis revealed an increase in c-src expression and identified subtle changes in the expression of genes regulated by thyroid hormones. Significant decreases in the circulating levels of T3 but not T4 hormone are consistent with this observation and reminiscent of euthyroid sick syndrome, a stress-associated clinical condition.

Interferon-gamma administration does not affect human thyroid hormone metabolism in the post-surgical euthyroid sick syndrome

Cytokines are thought to be involved in the pathogenesis the euthyroid sick syndrome. Experimental data from in vitro and animal in vivo studies suggest that interferon-gamma (IFN-gamma) could be another cytokine that might influence thyroid hormone metabolism, although in a previous study in healthy subjects we could not demonstrate an effect of IFN-gamma on thyroid hormone indices. Possibly, however, a non-stressed system is not a representative environment to study the effects of a mediator, which might exert its role during pathological circumstances in which it may interact synergistically with other inflammatory mediators. Therefore, we studied the effects of a single dose of recombinant human IFN-gamma (Immukine, 100 microg/m2, sc) on thyroid hormone concentrations in a placebo-controlled trial in 13 major surgery patients. Basal IFN-gamma levels did not increase. IFN-gamma induced a significant increase in monocyte HLA-DR expression (post-operative 50%; 24 h after IFN-gamma 90%), but did not affect thyroid hormone and thyroid stimulating hormone concentrations. We therefore conclude that IFN-gamma does not appear to be involved in the major changes in thyroid hormone metabolism in patients with non-thyroidal illness.

Rapid and transient reduction in circulating thyroid hormones following systemic antigen priming: implications for functional collaboration between dendritic cells and thyroid

The thyroid hormones T(3) (tri-iodothyronine) and T(4) (thyroxine) are disseminated throughout the body via the circulation and are maintained across a range of physiological concentrations under the control of thyroid-stimulating hormone (TSH). T(3) (and T(4) after conversion to T(3)) influences many biological activities, including gene expression and protein synthesis, though little is known about the nature of pituitary-thyroid immune interactions. In the present study we show that serum T(3) and T(4) levels are sharply but transiently reduced during the first 24 h of systemic antigen exposure and that this is followed by suppressed levels of free T(4), after which there is rapid recovery to normal levels. Splenic dendritic cells, depending upon the stage of maturation/activation, were found to be a rich source of TSH, and CD11c(+) cells with dendritic cell morphology were present in the thyroid 1-3 days after antigen exposure. Moreover, antigen priming of hypophysectomized mice that are unable to make pituitary-derived TSH resulted in significant increases in circulating T(4), implying that compensation in the drop in thyroid hormones can be regulated from extrapituitary sources. These findings thus identify a novel set of immune-endocrine interactions that transpire during the early phase of antigen exposure, and they suggest that under appropriate conditions the immune system directly participates in the process of maintaining physiological homeostasis by contributing to the regulatory control of thyroid hormone activity.

Regulation of hepatocyte thyroxine 5'-deiodinase by T3 and nuclear receptor coactivators as a model of the sick euthyroid syndrome

The syndrome of nonthyroidal illness, also known as the sick euthyroid syndrome, is characterized by a low plasma T3 and an "inappropriately normal" plasma thyrotropin in the absence of intrinsic disease of the hypothalamic-pituitary-thyroid axis. The syndrome is due in part to decreased activity of type I iodothyronine 5'-deiodinase (5' D-I), the hepatic enzyme that converts thyroxine to T3 and that is induced at the transcriptional level by T3. The hypothesis tested is that cytokines decrease T3 induction of 5' D-I, resulting in decreased T3 production and hence a further decrease in 5' D-I. The proposed mechanism is competition for limiting amounts of nuclear receptor coactivators between the 5' D-I promoter and the promoters of cytokine-induced genes. Using primary cultures of rat hepatocytes, we demonstrate that interleukins 1 and 6 inhibit the T3 induction of 5' D-I RNA and enzyme activity. This effect is at the level of transcription and can be partially overcome by exogenous steroid receptor coactivator-1 (SRC-1). The physical mass of endogenous SRC-1 is not affected by cytokine exposure, and exogenous SRC-1 does not affect 5' D-I in the absence of cytokines. The data support the hypothesis that cytokine-induced competition for limiting amounts of coactivators decreases hepatic 5' D-I expression, contributing to the etiology of the sick euthyroid syndrome.

A potential role of activated NF-kappa B in the pathogenesis of euthyroid sick syndrome

Euthyroid sick syndrome, characterized by low serum 3,5, 3'-triiodothyronine (T(3)) with normal L-thyroxine levels, is associated with a wide variety of disorders including sepsis, malignancy, and AIDS. The degree of low T(3) in circulation has been shown to correlate with the severity of the underlying disorders and with the prognosis. Elevated TNF-alpha levels, which accompany severe illness, are associated with decreased activity of type I 5'-deiodinase (5'-DI) in liver, leading us to speculate that high levels of this factor contribute to euthyroid sick syndrome. Here we demonstrate that the activation of NF-kappa B by TNF-alpha interferes with thyroid-hormone action as demonstrated by impairment of T(3)-dependent induction of 5'-DI gene expression in HepG2 cells. Inhibition of NF-kappa B action by a dominant-negative NF-kappa B reversed this effect and allowed T(3) induction of 5'-DI. Furthermore, we show that an inhibitor of NF-kappa B activation, clarithromycin (CAM), can inhibit TNF-alpha-induced activation of NF-kappa B and restore T(3)-dependent induction of 5'-DI mRNA and enzyme activity. These results suggest that NF-kappa B activation by TNF-alpha is involved in the pathogenesis of euthyroid sick syndrome and that CAM could help prevent a decrease in serum T(3) levels and thus ameliorate euthyroid sick syndrome.

Administration of interferon-gamma in healthy subjects does not modulate thyroid hormone metabolism

Cytokines, such as tumor necrosis factor-alpha (TNF-alpha), interleukin (IL-2), IL-6, and interferon-alpha (IFN-alpha), alter human thyroid hormone metabolism and may be involved in the pathogenesis the euthyroid sick syndrome. Experimental data suggest that interferon-gamma (IFN-gamma) could be another cytokine that might influence thyroid hormone metabolism. To evaluate whether IFN-gamma can be involved in the pathogenesis of the alterations in thyroid hormone metabolism in humans with nonendocrine illness, we measured thyroid hormone concentrations in six healthy volunteers during 24 hours in a placebo controlled trial: once after subcutaneous administration of IFN-gamma (Immukine, [Boehringer Ingelheim GmbH, Ingelheim/Rheim, Germany] 100 microg/m2 subcutaneous) and once after the administration of saline (control). In addition, we measured cytokine concentrations in plasma (TNF-alpha and IL-6). IFN-gamma did not induce effects on any of the measured thyroid hormone and thyroid-stimulating hormone (TSH) plasma concentrations. Moreover, IFN-gamma did not affect TNF-alpha plasma levels. Only a modest but significant elevation of plasma IL-6 levels was detected after administration of IFN-gamma (p < 0.05 vs. control). It is concluded that IFN-gamma administration to healthy humans does not result in short term alterations of thyroid hormone metabolism. These data do therefore not support a role of IFN-gamma in the pathogenesis of the euthyroid sick syndrome in humans as might be deduced from in vitro and in vivo animal studies.

Effect of endotoxin challenge on hepatic 5'-deiodinase activity in cattle

Thyroid status is compromised in a variety of acute and chronic infections and toxin-mediated disease states. Conversion of thyroxine (T4) into the metabolically active hormone, triiodothyronine (T3), is catalyzed by 5'-deiodinase (5'D). Our objective was to determine the effect of endotoxin (LPS) challenge with and without L-arginine (Arg) infusion on hepatic activity of 5'D and plasma concentrations of T4 and T3. In a 2 x 2 factorial, beef heifers (275-310 kg b.wt.) were fed low (8% CP; 6.5 kg/d) or high (14% CP; 7.2 kg/d) isocaloric protein diets (1.96 Mcal/kg DM) for 10 d before LPS challenge. L-Arginine in saline (0.5 g/kg b.wt.) or saline alone was infused i.v. throughout an 8 hr period starting 2 hr before bolus LPS injection (Escherichia coli, 055: B5; 0.2 microg/kg; i.v.). Blood samples were collected at -2, 0, 3, 6, 12, and 24 hr relative to LPS injection. Liver samples were obtained 20 hr before, and then 6 and 24 hr after LPS challenge using a biopsy needle. Plasma T4 and T3 concentrations were not affected by dietary CP or Arg. Compared with levels at 0 hr, LPS challenge decreased plasma T4 (P < 0.01) and T3 (P < 0.001), respectively, 8.4% and 28.9% at 6 hr and 19.7% and 31.3% at 24 hr. Consistent with these changes, the T3:T4 ratio was lower than that at 0 hr (P < 0.001) 22.0% at 6 hr and 13.5% at 24 hr. Hepatic 5'D activities 20 hr before LPS injection were 2.80 +/- 0.11 nmol I- x hr(-1) x mg protein(-1) and decreased 24 hr after LPS, respectively, 45.4% (P < 0.01) and 17.6% (P < 0.05) in saline- and Arg-infused heifers. The results indicate that mild LPS challenge in cattle inhibits hepatic generation of T3 and decreases plasma concentrations of thyroid hormones. The data also suggest that the impact of LPS on 5'D activity in liver can be altered by Arg supplementation.

Expression of olfactory receptors during development in Xenopus laevis

A coordinated expression of tissue- and cell-specific genes during development is required to establish the complex functional organization of the vertebrate olfactory system. Owing to the unique features of its olfactory system and the well-characterized phases of its development, Xenopus laevis was chosen as a model organism to study the onset and the temporal and spatial patterns of expression of olfactory-specific genes. Using RT-PCR and in situ hybridization, it was found that expression of Xenopus olfactory marker protein and of class I receptors, which are thought to be responsible for the perception of water-soluble odorants, was detectable as early as stage 32, less than 2 days after fertilization. In contrast, expression of class II receptors, which are thought to recognize airborne odours, was not detected before stage 49, approximately 12 days after fertilization. The results indicate that the expression of olfactory receptors and marker protein is governed by temporally regulated cues during development.