Effect of triiodothyronine on reactive oxygen species generation by leukocytes, indices of oxidative damage, and antioxidant reserve

The role of thyroid hormone in the renal immune microenvironment

Thyroid hormones are essential for proper kidney growth and development. The kidney is not only the organ of thyroid hormone metabolism but also the target organ of thyroid hormone. Kidney disease is a common type of kidney damage, mainly including different types of acute kidney injury, chronic kidney disease, diabetic nephropathy, lupus nephritis, and renal cell carcinoma. The kidney is often damaged by an immune response directed against its antigens or a systemic immune response. A variety of immune cells in the innate and adaptive immune systems, including neutrophils, macrophages, dendritic cells, T lymphocytes, and B lymphocytes, is essential for maintaining immune homeostasis and preventing autoimmune kidney disease. Recent studies have found that thyroid hormone plays an indispensable role in the immune microenvironment of various kidney diseases. Thyroid hormones regulate the activity of neutrophils, and dendritic cells express triiodothyronine receptors. Compared to hypothyroidism, hyperthyroidism has a greater effect on neutrophils. Furthermore, in adaptive immune systems, thyroid hormone may activate T lymphocytes through several underlying mechanisms, such as mediating NF-κB, protein kinase C signalling pathways, and β-adrenergic receptors, leading to increased T lymphocyte activation. The present review discusses the effects of thyroid hormone metabolism regulation in the immune microenvironment on the function of various immune cells, especially neutrophils, macrophages, dendritic cells, T lymphocytes, and B lymphocytes. Although there are not enough data at this stage to conclude the clinical relevance of these findings, thyroid hormone metabolism may influence autoimmune kidney disease by regulating the renal immune microenvironment.

Hashimoto's thyroiditis increases the risk of new-onset systemic lupus erythematosus: a nationwide population-based cohort study

BACKGROUND

Previous studies have shown systemic lupus erythematosus (SLE) patients had a significantly higher prevalence of thyroid diseases and hypothyroidism than matched controls, and some case reports showed SLE may occur after Hashimoto's thyroiditis (HT).

OBJECTIVE

This study aimed to investigate the subsequent risk of SLE in patients with HT.

METHODS

In this retrospective cohort study done by the Taiwan National Health Insurance Research Database, the HT group (exposure group) and the non-HT group (comparator group) were propensity score matched at a ratio of 1:2 by demographic data, comorbidities, medications, and the index date. We used Cox proportional hazards models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). Several sensitivity analyses were done for cross-validation of our findings.

RESULTS

We identified 15,512 HT patients and matched 31,024 individuals. The incidence rate ratio of SLE was 3.58 (95% CI, 2.43-5.28; p < 0.01). Several sensitivity analyses show adjusted hazard ratio (aHR) (CIs) of 4.35 (3.28-5.76), 4.39 (3.31-5.82), 5.11 (3.75-6.98), and 4.70 (3.46-6.38), consistent with the results of the main model.

CONCLUSION

Our study showed an increased risk of SLE in the HT group after adjustment for baseline characteristics, comorbidities, and medical confounders compared with the reference group.

The interplay of thyroid hormones and the immune system - where we stand and why we need to know about it

Over the past few years, growing evidence suggests direct crosstalk between thyroid hormones (THs) and the immune system. Components of the immune system were proposed to interfere with the central regulation of systemic TH levels. Conversely, THs regulate innate and adaptive immune responses as immune cells are direct target cells of THs. Accordingly, they express different components of local TH action, such as TH transporters or receptors, but our picture of the interplay between THs and the immune system is still incomplete. This review provides a critical overview of current knowledge regarding the interaction of THs and the immune system with the main focus on local TH action within major innate and adaptive immune cell subsets. Thereby, this review aims to highlight open issues which might help to infer the clinical relevance of THs in host defence in the context of different types of diseases such as infection, ischemic organ injury or cancer.

Thyroid Hormone and Deiodination in Innate Immune Cells

Thyroid hormone has recently been recognized as an important determinant of innate immune cell function. Highly specialized cells of the innate immune system, including neutrophils, monocytes/macrophages, and dendritic cells, are capable of identifying pathogens and initiating an inflammatory response. They can either phagocytose and kill microbes, or recruit other innate or adaptive immune cells to the site of inflammation. Innate immune cells derive from the hematopoietic lineage and are generated in the bone marrow, from where they can be recruited into the blood and tissues in the case of infection. The link between the immune and endocrine systems is increasingly well established, and recent studies have shown that innate immune cells can be seen as important thyroid hormone target cells. Tight regulation of cellular thyroid hormone availability and action is performed by thyroid hormone transporters, receptors, and the deiodinase enzymes. Innate immune cells express all these molecular elements of intracellular thyroid hormone metabolism. Interestingly, there is recent evidence for a causal relationship between cellular thyroid hormone status and innate immune cell function. This review describes the effects of modulation of intracellular thyroid hormone metabolism on innate immune cell function, specifically neutrophils, macrophages, and dendritic cells, with a special focus on the deiodinase enzymes. Although there are insufficient data at this stage for conclusions on the clinical relevance of these findings, thyroid hormone metabolism may partially determine the innate immune response and, by inference, the clinical susceptibility to infections.

The Role of Thyroid Hormone in the Innate and Adaptive Immune Response during Infection

In the past decades, there has been growing evidence for a functional interaction between the thyroid hormone and the immune system. This article provides an overview of the mechanisms by which thyroid hormones affect the innate and adaptive immune response during infection. The influence of thyroid hormone on the most important players of the innate [neutrophils, macrophages, natural killer (NK) cells, and dendritic cells (DCs)] and adaptive immune system (B- and T-lymphocytes) is reviewed here based on both clinical and preclinical studies. The effects of modulation of the immune system by drugs, such as monoclonal antibodies, tyrosine kinase inhibitors, and interferons on thyroid function, are beyond the scope of this article. Thyroid hormones regulate the activity of neutrophils which is reflected by higher numbers of neutrophils outside the bloodstream and enhanced activity of the respiratory burst following stimulation with thyroid hormone. Hyperthyroidism affects neutrophil function to a larger extent than hypothyroidism. In addition to neutrophil function, macrophage function is strongly affected by thyroid hormones, with triiodothyronine having a pro-inflammatory effect in these cells. NK cell proliferation and cytotoxic activity are also dependent on thyroid hormone levels. Finally, thyroid hormones enhance DC proliferation and maturation. In the adaptive immune system, a hyperthyroid state leads to increased activation of lymphocytes. This effect of thyroid hormone is mediated by various factors including NF-κB and protein kinase C signaling pathways and the β-adrenergic receptor. In general, a hyperthyroid state leads to a more activated immune system whereas hypothyroidism leads to a less activated immune system. © 2020 American Physiological Society. Compr Physiol 10:1277-1287, 2020.

Nongenomic Actions of Thyroid Hormone: The Integrin Component

The extracellular domain of plasma membrane integrin αvβ3 contains a cell surface receptor for thyroid hormone analogues. The receptor is largely expressed and activated in tumor cells and rapidly dividing endothelial cells. The principal ligand for this receptor is l-thyroxine (T₄), usually regarded only as a prohormone for 3,5,3'-triiodo-l-thyronine (T₃), the hormone analogue that expresses thyroid hormone in the cell nucleus via nuclear receptors that are unrelated structurally to integrin αvβ3. At the integrin receptor for thyroid hormone, T₄ regulates cancer and endothelial cell division, tumor cell defense pathways (such as anti-apoptosis), and angiogenesis and supports metastasis, radioresistance, and chemoresistance. The molecular mechanisms involve signal transduction via mitogen-activated protein kinase and phosphatidylinositol 3-kinase, differential expression of multiple genes related to the listed cell processes, and regulation of activities of other cell surface proteins, such as vascular growth factor receptors. Tetraiodothyroacetic acid (tetrac) is derived from T₄ and competes with binding of T₄ to the integrin. In the absence of T₄, tetrac and chemically modified tetrac also have anticancer effects that culminate in altered gene transcription. Tumor xenografts are arrested by unmodified and chemically modified tetrac. The receptor requires further characterization in terms of contributions to nonmalignant cells, such as platelets and phagocytes. The integrin αvβ3 receptor for thyroid hormone offers a large panel of cellular actions that are relevant to cancer biology and that may be regulated by tetrac derivatives.

Cell Type- and Sex-Specific Dysregulation of Thyroid Hormone Receptors in Placentas in Gestational Diabetes Mellitus

Thyroid hormones are essential for development of trophoblasts and the fetus. They also regulate a wide range of metabolic processes. We investigated the influence of maternal gestational diabetes mellitus (GDM) on thyroid hormone receptor (THR) isoforms THRα1, THRα2, THRβ1 and THRβ2 of the human placenta in a sex- and cell-type specific manner. Term placental tissue was obtained from women with (n = 40) or without GDM (control; n = 40). THRs levels were measured by semi-quantitative immunohistochemistry and real-time qRT-PCR. We localized THR immunostaining in syncytiotrophoblast (SCT), which was the tissue with the strongest signal. Double immunofluorescence identified THR in decidual cells in the stroma and in extravillous cytotrophoblasts. GDM did not change THRα1 immunolabelling intensity in decidua, but was associated with a stronger immunolabelling in SCT compared to GDM (p < 0.05). The SCT difference of GDM vs. control was strongest (p < 0.01) in female placentas. THRα2 was only weakly present and immunolabelling was weaker (p < 0.05) in SCT of only male GDM placentas in comparison to male controls. THRβ1/β2 immunostaining was weak in all cell types without changes in GDM. However, more THRβ1/2 protein was present (p < 0.001) in male than female placentas. All these protein changes were paralleled by changes of THR transcript levels. The data show that THR are expressed in term trophoblast in relation to fetal sex. Maternal GDM influences predominantly THRα1 in SCT, with the strongest GDM effect in SCT of female placentas.

Thyroid Hormone Action on Innate Immunity

The interplay between thyroid hormone action and the immune system has been established in physiological and pathological settings. However, their connection is complex and still not completely understood. The thyroid hormones (THs), 3,3',5,5' tetraiodo-L-thyroxine (T4) and 3,3',5-triiodo-L-thyronine (T3) play essential roles in both the innate and adaptive immune responses. Despite much research having been carried out on this topic, the available data are sometimes difficult to interpret or even contradictory. Innate immune cells act as the first line of defense, mainly involving granulocytes and natural killer cells. In turn, antigen presenting cells, macrophages and dendritic cells capture, process and present antigens (self and foreign) to naïve T lymphocytes in secondary lymphoid tissues for the development of adaptive immunity. Here, we review the cellular and molecular mechanisms involved in T4 and T3 effects on innate immune cells. An overview of the state-of-the-art of TH transport across the target cell membrane, TH metabolism inside these cells, and the genomic and non-genomic mechanisms involved in the action of THs in the different innate immune cell subsets is included. The present knowledge of TH effects as well as the thyroid status on innate immunity helps to understand the complex adaptive responses achieved with profound implications in immunopathology, which include inflammation, cancer and autoimmunity, at the crossroads of the immune and endocrine systems.

Regulation of Intracellular Triiodothyronine Is Essential for Optimal Macrophage Function

Innate immune cells, including macrophages, have recently been identified as target cells for thyroid hormone. We hypothesized that optimal intracellular concentrations of the active thyroid hormone triiodothyronine (T3) are essential for proinflammatory macrophage function. T3 is generated intracellularly by type 2 deiodinase (D2) and acts via the nuclear thyroid hormone receptor (TR). In zebrafish embryos, D2 knockdown increased mortality during pneumococcal meningitis. Primary murine D2 knockout macrophages exhibited impaired phagocytosis and partially reduced cytokine response to stimulation with bacterial endotoxin. These effects are presumably due to reduced intracellular T3 availability. Knockdown of the main TR in macrophages, TRα, impaired polarization into proinflammatory macrophages and amplified polarization into immunomodulatory macrophages. Intracellular T3 availability and action appear to play a crucial role in macrophage function. Our data suggest that low intracellular T3 action has an anti-inflammatory effect, possibly due to an effect on macrophage polarization mediated via the TRα. This study provides important insights into the link between the endocrine and innate immune system.

Thyroid hormone metabolism in innate immune cells

Thyroid hormone (TH) metabolism and thyroid status have been linked to various aspects of the immune response. There is extensive literature available on the effects of thyroid hormone on innate immune cells. However, only recently have authors begun to study the mechanisms behind these effects and the role of intracellular TH metabolism in innate immune cell function during inflammation. This review provides an overview of the molecular machinery of intracellular TH metabolism present in neutrophils, macrophages and dendritic cells and the role and effects of intracellular TH metabolism in these cells. Circulating TH levels have a profound effect on neutrophil, macrophage and dendritic cell function. In general, increased TH levels result in an amplification of the pro-inflammatory response of these cells. The mechanisms behind these effects include both genomic and non-genomic effects of TH. Besides a pro-inflammatory effect induced by extracellular TH, the cellular response to pro-inflammatory stimuli appears to be dependent on functional intracellular TH metabolism. This is illustrated by the fact that the deiodinase enzymes and in some cell types also thyroid hormone receptors appear to be crucial for adequate innate immune cell function. This overview of the literature suggests that TH metabolism plays an important role in the host defence against infection through the modulation of innate immune cell function.

The Thyroid Hormone Inactivating Enzyme Type 3 Deiodinase is Present in Bactericidal Granules and the Cytoplasm of Human Neutrophils

Neutrophils are important effector cells of the innate immune system. Thyroid hormone (TH) is thought to play an important role in their function. Intracellular TH levels are regulated by the deiodinating enzymes. The TH-inactivating type 3 deiodinase (D3) is expressed in infiltrating murine neutrophils, and D3 knockout mice show impaired bacterial killing upon infection. This suggests that D3 plays an important role in the bacterial killing capacity of neutrophils. The mechanism behind this effect is unknown. We aimed to assess the presence of D3 in human neutrophils, and determine its subcellular localization using confocal and electron microscopy, because this could give important clues about its function in these cells. D3 appeared to be present in the cytoplasm and in myeloperoxidase containing azurophilic granules and as well as lactoferrin containing specific granules within human neutrophils. This subcellular localization did not change upon activation of the cells. D3 is observed intracellularly during neutrophil extracellular trap formation, followed by a reduction of D3 staining after release of the neutrophil extracellular traps into the extracellular space. At the transcriptional level, human neutrophils expressed additional essential elements of TH metabolism, including TH transporters and TH receptors. Here, we demonstrate the presence and subcellular location of D3 in human neutrophils for the first time and propose a model, in which D3 plays a role in the bacterial killing capacity of neutrophils either through generation of iodide for the myeloperoxidase system or through modulation of intracellular TH bioavailability.

Role of Tyrosine Isomers in Acute and Chronic Diseases Leading to Oxidative Stress - A Review

Oxidative stress plays a major role in the pathogenesis of a variety of acute and chronic diseases. Measurement of the oxidative stress-related end products may be performed, e.g. that of structural isomers of the physiological para-tyrosine, namely meta- and ortho-tyrosine, that are oxidized derivatives of phenylalanine. Recent data suggest that in sepsis, serum level of meta-tyrosine increases, which peaks on the 2(nd) and 3(rd) days (p<0.05 vs. controls), and the kinetics follows the intensity of the systemic inflammation correlating with serum procalcitonin levels. In a similar study subset, urinary meta-tyrosine excretion correlated with both need of daily insulin dose and the insulin-glucose product in non-diabetic septic cases (p<0.01 for both). Using linear regression model, meta-tyrosine excretion, urinary meta-tyrosine/para-tyrosine, urinary ortho-tyrosine/para-tyrosine and urinary (meta- + orthotyrosine)/ para-tyrosine proved to be markers of carbohydrate homeostasis. In a chronic rodent model, we tried to compensate the abnormal tyrosine isomers using para-tyrosine, the physiological amino acid. Rats were fed a standard high cholesterol-diet, and were given para-tyrosine or vehicle orally. High-cholesterol feeding lead to a significant increase in aortic wall meta-tyrosine content and a decreased vasorelaxation of the aorta to insulin and the glucagon-like peptide-1 analogue, liraglutide, that both could be prevented by administration of para-tyrosine. Concluding, these data suggest that meta- and ortho-tyrosine are potential markers of oxidative stress in acute diseases related to oxidative stress, and may also interfere with insulin action in septic humans. Competition of meta- and ortho-tyrosine by supplementation of para-tyrosine may exert a protective role in oxidative stress-related diseases.

Dry olive leaf extract counteracts L-thyroxine-induced genotoxicity in human peripheral blood leukocytes in vitro

The thyroid hormones change the rate of basal metabolism, modulating the consumption of oxygen and causing production of reactive oxygen species, which leads to the development of oxidative stress and DNA strand breaks. Olive (Olea europaea L.) leaf contains many potentially bioactive compounds, making it one of the most potent natural antioxidants. The objective of this study was to evaluate the genotoxicity of L-thyroxine and to investigate antioxidative and antigenotoxic potential of the standardized oleuropein-rich dry olive leaf extract (DOLE) against hydrogen peroxide and L-thyroxine-induced DNA damage in human peripheral blood leukocytes by using the comet assay. Various concentrations of the extract were tested with both DNA damage inducers, under two different experimental conditions, pretreatment and posttreatment. Results indicate that L-thyroxine exhibited genotoxic effect and that DOLE displayed protective effect against thyroxine-induced genotoxicity. The number of cells with DNA damage, was significantly reduced, in both pretreated and posttreated samples (P < 0.05). Comparing the beneficial effect of all tested concentrations of DOLE, in both experimental protocols, it appears that extract was more effective in reducing DNA damage in the pretreatment, exhibiting protective role against L-thyroxine effect. This feature of DOLE can be explained by its capacity to act as potent free radical scavenger.

A comparative genotoxicity study of a supraphysiological dose of triiodothyronine (T₃) in obese rats subjected to either calorie-restricted diet or hyperthyroidism

This study was designed to determine the genotoxicity of a supraphysiological dose of triiodothyronine (T₃) in both obese and calorie-restricted obese animals. Fifty male Wistar rats were randomly assigned to one of the two following groups: control (C; n = 10) and obese (OB; n = 40). The C group received standard food, whereas the OB group was fed a hypercaloric diet for 20 weeks. After this period, half of the OB animals (n = 20) were subjected to a 25%-calorie restriction of standard diet for 8 weeks forming thus a new group (OR), whereas the remaining OB animals were kept on the initial hypercaloric diet. During the following two weeks, 10 OR animals continued on the calorie restriction diet, whereas the remaining 10 rats of this group formed a new group (ORS) given a supraphysiological dose of T₃ (25 µg/100 g body weight) along with the calorie restriction diet. Similarly, the remaining OB animals were divided into two groups, one that continued on the hypercaloric diet (OB, n = 10), and one that received the supraphysiological dose of T₃ (25 µg/100 g body weight) along with the hypercaloric diet (OS, n = 10) for two weeks. The OB group showed weight gain, increased adiposity, insulin resistance, increased leptin levels and genotoxicity; T₃ administration in OS animals led to an increase in genotoxicity and oxidative stress when compared with the OB group. The OR group showed weight loss and normalized levels of adiposity, insulin resistance, serum leptin and genotoxicity, thus having features similar to those of the C group. On the other hand, the ORS group, compared to OR animals, showed higher genotoxicity. Our results indicate that regardless of diet, a supraphysiological dose of T₃ causes genotoxicity and potentiates oxidative stress.

Nongenomic effects of thyroid hormones on the immune system cells: New targets, old players

It is now widely accepted that thyroid hormones, l-thyroxine (T(4)) and 3,3',5-triiodo-l-thyronine (T(3)), act as modulators of the immune response. Immune functions such as chemotaxis, phagocytosis, generation of reactive oxygen species, and cytokine synthesis and release, are altered in hypo- and hyper-thyroid conditions, even though for many immune cells no clear correlation has been found between altered levels of T(3) or T(4) and effects on the immune responses. Integrins are extracellular matrix proteins that are important modulators of many cellular responses, and the integrin αvβ3 has been identified as a cell surface receptor for thyroid hormones. Rapid signaling via this plasma membrane binding site appears to be responsible for many nongenomic effects of thyroid hormones, independent of the classic nuclear receptors. Through the integrin αvβ3 receptor the hormone can activate both the ERK1/2 and phosphatidylinositol 3-kinase pathways, with downstream effects including intracellular protein trafficking, angiogenesis and tumor cell proliferation. It has recently become clear that an important downstream target of the thyroid hormone nongenomic pathway may be the mammalian target of rapamycin, mTOR. New results demonstrate the capability of T(3) or T(4) to induce in the short time range important responses related to the immune function, such as reactive oxygen species production and cell migration in THP-1 monocytes. Thus thyroid hormones seem to be able to modulate the immune system by a combination of rapid nongenomic responses interacting with the classical nuclear response.

Thyroid hormones as modulators of immune activities at the cellular level

BACKGROUND

Increasing evidence suggests that thyroid hormones, L-thyroxine (T(4)) and 3,3',5-triiodo-L-thyronine (T(3)), are modulators of the immune response. In monocytes, macrophages, leukocytes, natural killer cells, and lymphocytes, a wide range of immune functions such as chemotaxis, phagocytosis, generation of reactive oxygen species (ROS), and cytokine synthesis and release are altered under hypo- and hyperthyroid conditions.

SUMMARY

Hyperthyroidism decreases the proinflammatory activities of monocytes and macrophages, whereas enhancement of phagocytosis and increased levels of ROS may occur during hypothyroidism. The expression of proinflammatory molecules such as macrophage inflammatory protein-1α and interleukin-1β increases in hypothyroidism. However, in Kupffer cells, proinflammatory activities such as the respiratory burst, nitric oxide synthase activity, and tumor necrosis factor-α expression may result from increased T(3) levels. Thyroid hormones also affect natural killer cell activity and cell-mediated immune responses. Still, for many immune cells no clear correlation has been found so far between abnormally high or low T(3) or T(4) levels and the effects observed on the immune responses.

CONCLUSIONS

In this review we outline the contributions of thyroid hormones to different aspects of innate and adaptive immune responses. The relationship between thyroid hormones and immune cells is complex and T(3) and T(4) may modulate immune responses through both genomic and nongenomic mechanisms. Future studies of the molecular signaling mechanisms involved in this cross-talk between thyroid hormones and the immune system may support development of new strategies to improve clinical immune responses.

Decreased number of circulating endothelial progenitor cells in patients with Graves' hyperthyroidism

OBJECTIVE

A relevant biological role of circulating endothelial progenitor cells (EPC) was recently demonstrated. EPC are generated in the bone marrow, and interact with damaged endothelium, restoring the integrity of the monolayer. Therefore, aim of the present study was to evaluate EPC in the blood of patients with untreated Graves' hyperthyroidism (GD), in whom an increased oxidative stress was observed.

DESIGN AND METHODS

Twenty-three patients with untreated active GD and 18 matched normal controls (NC) were included in the study. Circulating EPC were isolated from peripheral blood. Mononuclear cells were cultured with endothelial basal medium supplemented with EGM SingleQuots, and were identified by positive double staining after 7 days in culture. Circulating levels of C reactive protein, total antioxidant power, interleukin (IL)-6, IL- 18, monocyte chemoattractant protein-1, tumor necrosis facotr- α, soluble vascular cell adhesion molecule (VCAM) and intracellular adhesion molecule were evaluated by enzymelinked immunosorbent assay kit. EPC number was also evaluated in a subgroup of GD patients after restoration of euthyroidism.

RESULTS

Systolic blood pressure resulted increased in GD patients compared with control subjects whereas diastolic blood pressure was not significantly different. Patients with GD showed an increase in circulating levels of IL-18 and VCAM-1 and a reduction of total antioxidant power (p<0.05) compared to NC. Moreover, a reduced number of EPC was observed in patients with GD compared to NC (p<0.05) which turned to NC values after restoring euthyroidism.

CONCLUSION

Patients with GD showed a reduction in the physiological protective mechanisms against endothelial damage, probably induced by increased inflammation and oxidative stress.

The role of allopurinol on oxidative stress in experimental hyperthyroidism

AIM

During hyperthyroidism, production of free oxygen radicals derives, where xanthine oxidase may also play an important role. Allopurinol, a xanthine oxidase inhibitor, has a significant effect on thyrotoxicosis-related oxidative stress. However, the relationship between thyroid hormones, oxidative stress parameters and allopurinol remains to be explored.

METHODS

Forty-two Wistar albino rats were divided into three groups. Rats in group A served as negative controls, while group B had untreated thyrotoxicosis and group C received allopurinol. Hyperthyroidism was induced by daily 0.2 mg/kg L-thyroxine intraperitoneally in groups B and C; 40 mg/kg allopurinol were given daily intraperitoneally. Efficacy of the treatment was assessed after 72 h and 21 days, by measuring serum xanthine oxidase (XO), malondialdehyde (MDA), glutathione (GSH), glutathione reductase (GR), glutathione peroxidase (GPx) and nitric oxide derivates (NO*x).

RESULTS

In both time periods, serum XO, MDA, GSH and NO*x levels were significantly increased after thyroid hormone induction (p<0.05). Levels of XO, MDA and NO*x decreased with allopurinol treatment (p<0.05). There was a remarkable decrease in triiodothyronine levels in group C after 72 h (p<0.05), and in both triiodothyronine and thyroxine levels in group C after 21 days (p<0.05). There was no difference between groups B and C in means of serum GSH, GR and GPx levels (p>0.05).

CONCLUSIONS

This study suggests an association between allopurinol and the biosynthesis of thyroid hormones. Allopurinol prevents the hyperthyroid state, which is mediated predominantly by triiodothyronine and not by XO. This issue has to be questioned in further studies where allopurinol is administered in control subjects.

The interaction of oxidative stress response with cytokines in the thyrotoxic rat: is there a link?

Oxidative stress is regarded as a pathogenic factor in hyperthyroidism. Our purpose was to determine the relationship between the oxidative stress and the inflammatory cytokines and to investigate how melatonin affects oxidative damage and cytokine response in thyrotoxic rats. Twenty-one rats were divided into three groups. Group A served as negative controls. Group B had untreated thyrotoxicosis, and Group C received melatonin. Serum malondialdehyde (MDA), glutathione (GSH), glutathione reductase (GR), glutathione peroxidase (GPx), and nitric oxide derivates (NO^•x), and plasma IL-6, IL-10, and TNF-alpha were measured. MDA, GSH, NO^•x, IL-10, and TNF-alpha levels increased after L-thyroxine induction. An inhibition of triiodothyronine and thyroxine was detected, as a result of melatonin administration. MDA, GSH, and NO^•x levels were also affected by melatonin. Lowest TNF-alpha levels were observed in Group C. This study demonstrates that oxidative stress is related to cytokine response in the thyrotoxic rat. Melatonin treatment suppresses the hyperthyroidism-induced oxidative damage as well as TNF-alpha response.

Urinary ortho-tyrosine excretion in diabetes mellitus and renal failure: Evidence for hydroxyl radical production

BACKGROUND

Phenylalanine is converted to para- and ortho-tyrosine by hydroxyl free radical, or to para-tyrosine by the phenylalanine hydroxylase enzyme. The aim of this study was to measure para- and ortho-tyrosine in the urine and plasma of patients with chronic renal disease and/or diabetes, to obtain information on the renal handling of the different tyrosine isomers and, furthermore, to measure urinary levels of 8-epi-prostaglandin-F(2alpha), a marker of lipid peroxidation.

METHODS

In our cross-sectional study we measured para-, ortho-tyrosine, and phenylalanine levels, using high performance liquid chromatography and 8-epi-prostaglandin-F(2alpha) with enzyme-linked immunosorbent assay (ELISA). We compared 4 groups: (1) controls (CONTR, N = 14), (2) patients with chronic kidney disease (CKD, N = 12), (3) patients with type 2 diabetes mellitus (DIAB, N = 17), (4) patients with chronic kidney disease and type 2 diabetes (DIAB-CKD, N = 19).

RESULTS

We found a decreased plasma para-tyrosine level and decreased urinary para-tyrosine excretion in CKD patients, while the fractional excretion of para-tyrosine was similar in all 4 groups, approximately 1%. There was no difference in the plasma ortho-tyrosine levels between the groups. However, urinary ortho-tyrosine excretion was higher in all 3 groups of patients than in the CONTR group, and higher in DIAB and in DIAB-CKD patients than in CKD patients. The fractional excretion of ortho-tyrosine was significantly higher in DIAB and in DIAB-CKD patients than in the CONTR group. The fractional excretion of ortho-tyrosine exceeded 100% in the 2 diabetic groups. Urinary 8-epi-prostaglandin-F(2alpha)/creatinine ratio did not correlate with urinary ortho-tyrosine excretion.

CONCLUSION

The difference between para-tyrosine levels of the groups is probably due to renal impairment, while there is indirect evidence for an increased tubular secretion or production of ortho-tyrosine in the kidney in diabetic patients with or without CKD.

Neutrophils from Brazilian patients with Graves' disease: some biochemical and functional aspects

Graves' disease shows important systemic inflammatory complications and has been considered to be systemic autoimmune thyroid, skeletal muscle and connective tissue syndrome. Neutrophils participate in the pathophysiology of the two major immune and inflammatory manifestations of the disease, ophthalmopathy and myxedema, and may worsen the inflammatory picture. In this study we analysed some biochemical and functional aspects of neutrophils in Graves' disease patients to assess their participation in these processes. The results show that the complement and/or Fcgamma receptor-mediated oxygen radical production by neutrophils was increased when patient cells were compared with controls. However the percentage of cells expressing complement and IgG receptors and the per-cell fluorescence, were similar, indicating that the increased oxidative burst was not due to an abnormal expression of mediating receptors. The production of hydrogen peroxide was also increased in hyperthyroid patient neutrophils as compared to controls. Conversely, antioxidant defences (superoxide dismutase activity and reduced glutathione content) in neutrophils from patients were not significantly different from healthy controls. The liberation of potent oxidative compounds together with the absence of adequate quenching of them by antioxidant mechanisms could be responsible for greater tissue damage in inflammatory conditions, as is the case in ophthalmopathy and myxedema patients. Considering our results and those of other workers, we encourage and suggest an associated antioxidant therapy to complement the conventional anti-thyroid therapy, especially in obvious inflammatory cases and in individuals who smoke.

The effect of the antioxidant catalase on oestrogens, triiodothyronine, and noradrenaline in the Comet assay

Metabolic changes in the phenolic groups of steroidal oestrogens accompanied by the generation of quinones and reactive oxygen species underlie their mutagenic effects. Although nonsteroidal hormones and related compounds have not been thoroughly investigated for genotoxicity, some of them also contain phenolic groups that could be involved in redox cycling. Therefore, the aim of the present study was to evaluate the possible DNA damaging effects of the thyroid hormone, triiodothyronine (T3), and the neurotransmitter, noradrenaline (NA), in human lymphocytes using the Comet assay. After dose-response investigations, doses of 100 microM T3 and 550 microM of NA, producing clear DNA damaging effects and good cell viability, were chosen for further experiments with the antioxidant, catalase. Since the scavenging enzyme catalase reduced the DNA damaging effects of T3 and NA, it can be concluded that T3 and NA induced DNA damage mainly via the production of reactive oxygen species. Therefore, the mechanism of mutagenic action of both steroidal hormones and nonsteroidal compounds, T3 and NA, imply the creation of oxidative stress and subsequent DNA damage with reactive oxygen species and, possibly, with reactive hormone derivatives created during their redox cycling.

Effect of chronic hypoxia on glutathione status and membrane integrity in the pancreas

BACKGROUND

Our recent study has shown that chronic hypoxia could upregulate significantly a local renin-angiotensin system in the pancreas. The activation of such a local renin-angiotensin system may provide an alternate mechanism that leads to the generation of reactive radical species in the pancreas during chronically hypoxic exposure. The present study aims at elucidating the antioxidant status in the pancreas during varying degrees of chronic hypoxia.

METHODS

Sprague-Dawley rats were exposed to an isobaric hypoxic (10% oxygen) chamber for a period up to 28 days. The glutathione status and membrane integrity of the pancreas were studied with a time course of chronic hypoxia (3, 7, 14, 21 and 28 days). The effect of chronic hypoxia on changes of oxidative states in the pancreas was assessed based on the measurements of glutathione, malondialdehyde, alpha-amylase and DNA fragmentation using biochemical assays.

RESULTS

Pancreatic glutathione was decreased drastically after 3-day hypoxia and its level was almost completely recovered after 7-day hypoxia. Malondialdehyde was not affected while DNA fragmentation was increased significantly in a time-dependent manner during the course of chronic hypoxia. Membrane integrity of the pancreatic cells was improved, as evidenced by the decrease of plasma alpha-amylase during the time-course study of chronic hypoxia.

CONCLUSION

Pancreatic glutathione was depleted only in the early period of chronic hypoxia followed by a rapid recovery, suggesting that adaptive response of the pancreas may occur during chronic hypoxia. The enhancement of glutathione-dependent antioxidant capacity during chronic hypoxia prevented oxidative damage to the membrane of the pancreatic cells.

The suppressive effect of dietary restriction and weight loss in the obese on the generation of reactive oxygen species by leukocytes, lipid peroxidation, and protein carbonylation

Increased reactive oxygen species generation by the leukocytes of the obese may be responsible for increased oxidative injury to lipids and proteins and, hence, atherosclerosis. We have investigated whether reactive oxygen species generation by leukocytes and other indexes of oxidative damage in the body fall with short-term dietary restriction and weight loss. Nine nondiabetic obese subjects (body mass index, 32.5-64.4 kg/m(2)), not taking any antioxidants, were put on a 1000-Cal diet. Fasting blood samples were taken at 0, 1, 2, 3, and 4 weeks and at 12 weeks after the cessation of dietary restriction. Blood samples were also obtained at 1 and 2 h after administration of 75 g oral glucose at 0 and 4 weeks. Mononuclear cells (MNC) and polymorphonuclear leukocytes (PMN) were isolated, and reactive oxygen species generation was measured. Plasma concentrations of thiobarbituric acid-reactive species (TBARS), 13-hydroxyoctadecadienoic acid (13-HODE), 9-hydroxyoctadecadienoic acid (9-HODE), carbonylated proteins, o-tyrosine, and m-tyrosine as indexes of oxidative damage to lipids, proteins and amino acids, respectively, were measured. Antioxidant vitamins were measured as indexes of antioxidant reserves. Plasma tumor necrosis factor-alpha concentrations were also measured. Mean weight loss was 2.4 +/- 0.6 kg at week 1, 2.5 +/- 1.7 kg at week 2, 3.9 +/- 0.8 kg at week 3, and 4.5 +/- 2.8 kg at week 4 (P < 0.05). Reactive oxygen species generation by PMN fell from 236.4 +/- 95.8 to 150.9 +/- 69.0, 125.9 +/- 24.3, 96.0 +/- 39.9, and 103.1 +/- 35.7 mV at weeks 1, 2, 3, and 4, respectively (P < 0.001). It increased 3 months after the cessation of dietary restriction to 270.0 +/- 274.3 mV. Reactive oxygen species generation by MNC fell from 187.8 +/- 75.0 to 101.7 +/- 64.5, 86.9 +/- 42.8, 63.8 +/- 14.3, and 75.1 +/- 32.2 mV and increased thereafter to 302.0 +/- 175.5 mV at 1, 2, 3, 4, and 16 weeks, respectively (P < 0.005). Reactive oxygen species generation by PMN and MNC increased in response to glucose; the relative increase was greater at 4 weeks than that at week 0 due to a fall in the basal levels of reactive oxygen species generation. Consistent with the fall in reactive oxygen species generation, there was a reduction in plasma TBARS from 1.68 +/- 0.17 micromol/L at week 0 to 1.47 micromol/L at 4 weeks (P < 0.05). The 13-HODE to linoleic acid ratio fell from a baseline of 100% to 56.4 +/- 36.1% at 4 weeks (P < 0.05), and the 9-HODE to linoleic acid ratio fell from a baseline of 100% to 60.5 +/- 37.7% at 4 weeks (P < 0.05). Carbonylated proteins fell from 1.39 +/- 0.27 microgram/mg protein at week 0 to 1.17 +/- 0.12 microgram/mg protein at week 4 (P < 0.05); o-tyrosine fell from 0.42 +/- 0.03 mmol/mol phenylalanine at week 0 to 0.36 +/- 0.02 mmol/mol phenylalanine at 4 weeks (P < 0.005), and m-tyrosine fell from 0.45 +/- 0.04 mmol/mol phenylalanine at week 0 to 0.40 +/- 0.03 mmol/mol phenylalanine at 4 weeks (P < 0.05). The basal concentrations of TBARS, 9-HODE, 13-HODE, carbonylated proteins, o-tyrosine, and m-tyrosine in the obese were significantly greater than those in normal subjects. On the other hand, tumor necrosis factor-alpha concentrations did not change during this 4-week period, nor was there any change in antioxidant vitamins. This is the first demonstration of 1) an increase in reactive oxygen species-induced damage in lipids, proteins, and amino acids in the obese compared with normal subjects; and 2) a decrease in reactive oxygen species generation by leukocytes and oxidative damage to lipids, proteins, and amino acids after dietary restriction and weight loss in the obese over a short period.