Lipid peroxidation and free radical scavengers in thyroid dysfunction in the rat: a possible mechanism of injury to heart and skeletal muscle in hyperthyroidism

Protective effect of Korean red ginseng water extract on levothyroxine-induced hyperthyroidism and propylthiouracil-induced hypothyroidism in rats

Background

Korean red ginseng extract (KRGE) (Family: Araliaceae) is one of the most widely used traditional herbs in Asia. Multiple studies have shown that KRGE has anti-inflammation, anti-fatigue, anti-obesity, anti-oxidant, and anti-cancer effects.

Methods

Sprague-Dawley rats were divided into five groups for PTU-induced hypothyroidism and six groups for LT4-induced hyperthyroidism. At the experiment's conclusion, rats were sacrificed, and blood, thyroid gland, and liver samples were collected. Body weight was recorded weekly, and serum hormone levels were assessed using enzyme-linked immunoassay. Thyroid gland and liver tissues were stained with hematoxylin and eosin. KRGE was prepared in 0.5% CMC and stored at 4 °C before administration.

Results

In the LT4-induced hyperthyroidism model, KRGE prevented decreases in body weight, thyroid gland weight, liver weight, serum glucose, and thyroid hormone levels compared to the PTU group. It also reduced increases in T3, T4, and serum aspartate aminotransferase levels after LT4 treatment. Additionally, KRGE improved thyroid gland and liver histopathology, effects not observed in the PTU-induced hypothyroidism model.

Conclusion

All things considered, our research points to KRGE's potential protective role in rat hyperthyroidism caused by LT4 by lowering thyroid hormone production.

Low Thyroid Hormones Level Attenuates Mitochondrial Dysfunction and Right Ventricular Failure in Pulmonary Hypertensive Rats

PURPOSE

This study is to investigate the repercussions of hypothyroidism in the pathophysiological progression of pulmonary arterial hypertension (PAH).

METHODS

While the control (CTL, n = 5) male Wistar rats received vehicle, PAH was induced with monocrotaline (MCT group, n = 15). Hypothyroidism was induced in a subset of rats by methimazole 3 weeks prior to the MCT injection (MMZ + MCT group, n = 15). Plasma thyroid hormones were measured by radioimmunoassay. Electrocardiographic, echocardiographic, and hemodynamic analyses were performed to evaluate the progression of PAH. Gene expression of antioxidant enzymes and cardiac hypertrophy markers were assessed by qPCR. Mitochondrial respiration, ATP levels, and ROS production were measured in right ventricular (RV) samples.

RESULTS

Plasma T3 and T4 decreased in both MCT and MMZ + MCT groups (p < 0.05). Right ventricular systolic pressure (RVSP) increased, and RV - dP/dt, + dP/dt, and contractility index decreased in the MCT versus the CTL group and remained within control levels in the MMZ + MCT group (p < 0.05). Relative RV weight, RV wall thickness, RV diastolic area, and relative lung weight were augmented in the MCT versus the CTL group, whereas all parameters were improved to the CTL levels in the MMZ + MCT group (p < 0.05). Only the MCT group exhibited an increased duration of QTc interval compared to the baseline period (p < 0.05). ADP-induced mitochondrial respiration and ATP levels were decreased, and ROS production was increased in MCT versus the CTL group (p < 0.05), while the MMZ + MCT group exhibited increased mitochondrial respiration versus the MCT group (p < 0.05).

CONCLUSION

Hypothyroidism attenuated the RV mitochondrial dysfunction and the pathophysiological progression of MCT-induced PAH.

Gender Differences of Antioxidant System and Thyroid Function in Depressed Adolescents with Non-Suicidal Self-Injury

Purpose

The aim of our study was to explore the relation between serum levels of non-enzymatic antioxidants, thyroid function with the risk of non-suicidal self-injury (NSSI) in depressed adolescents.

Patients and Methods

We retrospected the electronic records of 454 hospitalized patients aged 13-17 years old with a diagnosis of major depressive disorder (239 patients with NSSI and 215 subjects without NSSI), and collected their demographic and clinical information, including serum levels of total bilirubin (Tbil), uric acid (UA), free triiodothyronine (FT3), free thyroxine (FT4) and thyroid stimulating hormone (TSH).

Results

The incidence of NSSI was 52.6% among depressed adolescents aged 13-17, 57.1% in female and 38.5% in male. After using the propensity scoring method to exclude the influence of age between the two groups, it was found that patients with NSSI showed lower levels of Tbil (P=0.046) and UA (P=0.015) compared with those without NSSI. Logistic regression results showed that serum UA was associated with NSSI behavior in female patients (OR=0.995, 95% CI: 0.991-0.999, P=0.014), and TSH was associated with NSSI in male participants (OR=0.499, 95% CI: 0.267-0.932, P=0.029).

Conclusion

Female and male may have different pathological mechanisms of NSSI. NSSI is more likely to be related to antioxidant reaction in female adolescent patients, while more likely to be related to thyroid function in male depressed adolescent patients.

Is beta-carotene consumption associated with thyroid hormone levels?

The thyroid hormones play a pivotal role in various physiological processes, including growth, metabolism regulation, and reproduction. While non-modifiable factors are known to impact thyroid function, such as genetics and age, nutritional factors are also important. Diets rich in selenium and iodine are conventionally acknowledged to be beneficial for the production and release of thyroid hormones. Recent studies have suggested a potential link between beta-carotene, a precursor to vitamin A (retinol), and thyroid function. Beta-carotene is known for its antioxidant properties and has been shown to play a role in the prevention of various clinical conditions such as cancer and cardiovascular and neurological diseases. However, its impact on thyroid function is still unclear. Some studies have suggested a positive association between beta-carotene levels and thyroid function, while others have found no significant effect. Conversely, the hormone produced by the thyroid gland, thyroxine, enhances the conversion of beta-carotene to retinol. Furthermore, vitamin A derivatives are being explored as potential therapeutic options for thyroid malignancies. In this review, we highlight the mechanisms through which beta-carotene/retinol and thyroid hormones interact and review the findings of clinical studies examining the association between beta-carotene consumption and thyroid hormone levels. Our review underscores the need for further research to clarify the relationship between beta-carotene and thyroid function.

Role of thyroid hormones-induced oxidative stress on cardiovascular physiology

Thyroid hormones (THs) play an essential role in the maintenance of cardiovascular homeostasis and are involved in the modulation of cardiac contractility, heart rate, diastolic function, systemic vascular resistance, and vasodilation. THs have actions on cardiovascular physiology through the activation or repression of target genes or the activation of intracellular signals through non-genomic mechanisms. Hyperthyroidism alters certain intracellular pathways involved in the preservation of the structure and functionality of the heart, causing relevant cardiovascular disorders. Reactive oxygen species (ROS) play an important role in the cardiovascular system, but the exacerbated increase in ROS caused by chronic hyperthyroidism together with regulation on the antioxidant system have been associated with the development of cardiovascular dysfunction. In this review, we analyze the role of THs-induced oxidative stress in the cellular and molecular changes that lead to cardiac dysfunction, as well as the effectiveness of antioxidant treatments in attenuating cardiac abnormalities developed during hyperthyroidism.

Functional State of Rat Heart Mitochondria in Experimental Hyperthyroidism

In this work, the effect of thyroxine on energy and oxidative metabolism in the mitochondria of the rat heart was studied. Hyperthyroidism was observed in experimental animals after chronic administration of T₄, which was accompanied by an increase in serum concentrations of free triiodothyronine (T₃) and thyroxine (T₄) by 1.8 and 3.4 times, respectively. The hyperthyroid rats (HR) had hypertrophy of the heart. In HR, there was a change in the oxygen consumption in the mitochondria of the heart, especially when using palmitoylcarnitine. The assay of respiratory chain enzymes revealed that the activities of complexes I, I + III, III, IV increased, whereas the activities of complexes II, II + III decreased in heart mitochondria of the experimental animals. It was shown that the level of respiratory complexes of the electron transport chain in hyperthyroid rats increased, except for complex V, the quantity of which was reduced. The development of oxidative stress in HR was observed: an increase in the hydrogen peroxide production rate, increase in lipid peroxidation and reduced glutathione. The activity of superoxide dismutase in the heart of HR was higher than in the control. At the same time, the activity of glutathione peroxidase decreased. The obtained data indicate that increased concentrations of thyroid hormones lead to changes in energy metabolism and the development of oxidative stress in the heart of rats, which in turn contributes to heart dysfunction.

Efficacy of using a complex of minerals and vitamins for prevention of complications in bone tissue and the digestive tract in rats with hypothyroidism

Significant consequences of hypothyroidism are impairments in all types of metabolism, including bone metabolism, pathological changes in the digestive tract and the development of deficiency of vitamins, macro-and micronutrients.The relevance of the study is due to the widespread occurrence of hypothyroidism and the feasibility of developing effective methods for the prevention of the pathology and its complications. The study was aimed at the condition of bone tissue and digestive tract in rats with hypothyroidism, as well as the effectiveness of preventive addition of a complex of vitamins and minerals. The studies were performed on rats with hypothyroidism that was caused using thyrostatic mercazolyl for 50 days, administered orally. Prophylaxis was performed by adding a prophylactic complex of vitamins P, C, D and minerals Ca, Mg, Cu, Se, Mn to the daily diet. In the bone tissue of rats, the indicators of destruction (elastase and acid phosphatase activity) and mineralization (alkaline phosphatase activity, calcium content) as well as the antioxidant state (activities of catalase, glutathione reductase, malonic dialdehyde content) were studied. In the gums and mucous membranes of the digestive tract of rats, we determined indicators of antioxidant status (catalase activity, malonic dialdehydecontent), inflammation (activities of elastase, acid phosphatase) and dysbiosis (activities of urease activity, lysozyme). In the bone tissue of rats with hypothyroidism, activation of destruction processes, reduction of calcium levels, activation of lipid peroxidation and antioxidant enzymes were found. Hypothyroidism also led to pathological disorders in the gums of rats and gastric mucosa, small and large intestine, namely – the development of inflammation, increased membrane permeability, activation of lipid peroxidation, increased contamination with opportunistic bacteria against the background of reduced antioxidant protection. In general, preventive use of the complex contributed to the normalization of the studied parameters in the gums, mucous membranes of the stomach, intestines, as well as remodeling processes and antioxidant-prooxidative state in the bone tissue of animals with hypothyroidism. In the conditions of hypothyroidism, the proposed complex of vitamins and minerals provided notable antioxidant, anti-inflammatory and antidysbiotic effects in the tissues of the gastrointestinal tract, thus overcoming the calcium deficiency in the blood and stopping the destructive and oxidative processes in the bone tissue of animals with hypothyroidism.

Angiotensin-(1-7) prevents T3-induced cardiomyocyte hypertrophy by upregulating FOXO3/SOD1/catalase and downregulating NF-ĸB

Clinical studies have shown a correlation between thyroid disorders and cardiac diseases. High levels of triiodothyronine (T3) induce cardiac hypertrophy, a risk factor for cardiac complications and heart failure. Previous results have demonstrated that angiotensin-(1-7) is able to block T3-induced cardiac hypertrophy; however, the molecular mechanisms involved in this event have not been fully elucidated. Here, we evidenced the contribution of FOXO3 signaling to angiotensin-(1-7) effects. Angiotensin-(1-7) treatment increased nuclear FOXO3 levels and reduced p-FOXO3 levels (inactive form) in isolated cardiomyocytes. Knockdown of FOXO3 by RNA silencing abrogated the antihypertrophic effect of angiotensin-(1-7). Increased expression of antioxidant enzymes superoxide dismutase 1 (SOD1 and catalase) and lower levels of reactive oxygen species and nuclear factor-κB (NF-κB) were observed after angiotensin-(1-7) treatment in vitro. Consistent with these results, transgenic rats overexpressing angiotensin-(1-7) displayed increased nuclear FOXO3 and SOD1 levels and reduced NF-κB levels in the heart. These results provide a new molecular mechanism responsible for the antihypertrophic effect of angiotensin-(1-7), which may contribute to future therapeutic targets.

Manipulation of Prenatal Thyroid Hormones Does Not Affect Growth or Physiology in Nestling Pied Flycatchers

Hormones transferred from mothers to their offspring are thought to be a tool for mothers to prepare their progeny for expected environmental conditions, thus increasing fitness. Thyroid hormones (THs) are crucial across vertebrates for embryonic and postnatal development and metabolism. Yet yolk THs have mostly been ignored in the context of hormone-mediated maternal effects. In addition, the few studies on maternal THs have yielded contrasting results that could be attributed to either species or environmental differences. In this study, we experimentally elevated yolk THs (within the natural range) in a wild population of a migratory passerine, the European pied flycatcher (Ficedula hypoleuca), and assessed the effects on hatching success, nestling survival, growth, and oxidative status (lipid peroxidation, antioxidant enzyme activity, and oxidative balance). We also sought to compare our results with those of a closely related species, the collared flycatcher (Ficedula albicolis), that has strong ecological and life-history similarities with our species. We found no effects of yolk THs on any of the responses measured. We could detect only a weak trend on growth: elevated yolk THs tended to increase growth during the second week after hatching. Our results contradict the findings of previous studies, including those of the collared flycatcher. However, differences in fledging success and nestling growth between both species in the same year suggest a context-dependent influence of the treatment. This study should stimulate more research on maternal effects mediated by THs and their potential context-dependent effects.

Selenium in the Treatment of Graves' Hyperthyroidism and Eye Disease

Based on the role of oxidative stress in the pathogenesis of Graves' hyperthyroidism (GH) and Graves' Orbitopathy (GO), a therapy with the antioxidant agent selenium has been proposed and a number of studies have been performed, both in vitro and in vivo. In GH, reactive oxygen species (ROS) contribute to the thyroid and peripheral tissues damage. In GO, tissue hypoxia, as well as ROS, are involved in the typical changes that occur in fibroadipose orbital tissue and the perimysium of extraocular muscles. Antioxidants have been proposed to improve the effects of antithyroid drugs in GH patients, as well as the remodeling of orbital tissues in patients with GO. Here, we reviewed the literature on the possible beneficial effects and clinical use of selenium in the management of patients with GH and GO. A randomized clinical trial on the use of selenium in patients with mild GO provided evidence for a beneficial effect; no data are available on more severe forms of GO. Although the real effectiveness of selenium in patients with GH remains questionable, its use in the management of mild GO is generally believed to be beneficial, and selenium administration has been included in the clinical practice for the patients with mild eye disease.

Prospective role of thyroid disorders in monitoring COVID-19 pandemic

COVID-19 pandemic has affected more than 200 countries and 1.3 million individuals have deceased within eleven months. Intense research on COVID-19 occurrence and prevalence enable us to understand that comorbidities play a crucial role in spread and severity of SARS-CoV-2 infection. Chronic kidney disease, diabetes, respiratory diseases and hypertension are among the various morbidities that are prevalent in symptomatic COVID-19 patients. However, the effect of altered thyroid-driven disorders cannot be ignored. Since thyroid hormone critically coordinate and regulate the major metabolism and biochemical pathways, this review is on the potential role of prevailing thyroid disorders in SARS-CoV-2 infection. Direct link of thyroid hormone with several disorders such as diabetes, vitamin D deficiency, obesity, kidney and liver disorders etc. suggests that the prevailing thyroid conditions may affect SARS-CoV-2 infection. Further, we discuss the oxidative stress-induced aging is associated with the degree of SARS-CoV-2 infection. Importantly, ACE2 protein which facilitates the host-cell entry of SARS-CoV-2 using the spike protein, are highly expressed in individuals with abnormal level of thyroid hormone. Altogether, we report that the malfunction of thyroid hormone synthesis may aggravate SARS-CoV-2 infection and thus monitoring the thyroid hormone may help in understanding the pathogenesis of COVID-19.

Evolution of the Knowledge of Free Radicals and Other Oxidants

Free radicals are chemical species (atoms, molecules, or ions) containing one or more unpaired electrons in their external orbitals and generally display a remarkable reactivity. The evidence of their existence was obtained only at the beginning of the 20th century. Chemists gradually ascertained the involvement of free radicals in organic reactions and, in the middle of the 20th century, their production in biological systems. For several decades, free radicals were thought to cause exclusively damaging effects . This idea was mainly supported by the finding that oxygen free radicals readily react with all biological macromolecules inducing their oxidative modification and loss of function. Moreover, evidence was obtained that when, in the living organism, free radicals are not neutralized by systems of biochemical defences, many pathological conditions develop. However, after some time, it became clear that the living systems not only had adapted to the coexistence with free radicals but also developed methods to turn these toxic substances to their advantage by using them in critical physiological processes. Therefore, free radicals play a dual role in living systems: they are toxic by-products of aerobic metabolism, causing oxidative damage and tissue dysfunction, and serve as molecular signals activating beneficial stress responses. This discovery also changed the way we consider antioxidants. Their use is usually regarded as helpful to counteract the damaging effects of free radicals but sometimes is harmful as it can block adaptive responses induced by low levels of radicals.

Energy metabolism and oxidative status of rat liver mitochondria in conditions of experimentally induced hyperthyroidism

The aim of the present work was to investigate the energy metabolism and antioxidant status of rat liver mitochondria using a model of hyperthyroidism. In experimental animals, the level of triiodothyronine and thyroxine was increased 3- and 4-fold, respectively, in comparison with that in the control group, indicating the development of hyperthyroidism in these animals. Oxygen consumption was found to be higher in rats with experimentally induced hyperthyroidism (from 20 to 60% depending on the experimental scheme used), with a slight decrease in the efficiency of oxidative phosphorylation and respiratory state ratio. It was shown for the first time that the level the respiratory complexes of the electron transport chain in hyperthyroid rats increased; however, the quantity of complexes III and V changed unreliably. The assay of respiratory chain enzymes revealed that the activities of complexes I, II, and citrate synthase increased, whereas the activities complexes II + III, III, IV decreased in liver mitochondria of the experimental animals. Alterations in the oxidative state in liver mitochondria were found: a 60% increase in the hydrogen peroxide production rate and a 45% increase in lipid peroxidation. The activities of superoxide dismutase and catalase in the liver of experimental rats were higher than in the control. At the same time, the activity of glutathione peroxidase did not change. The data obtained indicate that the known activation of metabolism and changes in the oxidative status in thyrotoxicosis are associated with variations in the respiratory chain functioning and the antioxidant enzymes of mitochondria.

Impact of hyperthyroidism on cardiac hypertrophy

The cardiac growth process (hypertrophy) is a crucial phenomenon conserved across a wide array of species and it is critically involved in maintenance of cardiac homeostasis. This process enables organism adaptation to changes of systemic demand and occurs due to a plethora of responses, depending on the type of signal or stimuli received. The growth of cardiac muscle cells in response to environmental conditions depends on the type, strength and duration of stimuli, and results in adaptive physiologic response or non-adaptive pathologic response. Thyroid hormones (TH) have a direct effect on the heart and induce a cardiac hypertrophy phenotype, which may evolve to heart failure. In this review, we summarize the literature on TH function in heart presenting results from experimental studies. We discuss the mechanistic aspects of TH associated with cardiac myocyte hypertrophy, increased cardiac myocyte contractility and electrical remodeling as well as the signaling pathways associated. In addition to classical crosstalk with the Sympathetic Nervous System (SNS), emerging work points to the new endocrine interaction between TH and Renin-Angiotensin System (RAS) is also explored. Given the inflammatory potential of the angiotensin II peptide, this new interaction may open the door for new therapeutic approaches that target key mechanisms responsible for TH-induced cardiac hypertrophy.

Synergistic nourishing 'Yin' effect of iridoid and phenylpropanoid glycosides from Radix Scrophulariae in vivo and in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

Radix Scrophulariae (RS), is a renowned traditional Chinese medicine used as nourishing 'Yin'. The iridoid glycosides (IG) and phenylpropanoid glycosides (PG) are main chemical constituents in RS. However, there had been no pharmacological experiment studies of synergy between IG and PG. Due to the constituents interactions, exploring their synergy profile is of great important for explaining the essence of nourishing 'Yin' efficacy of RS.

AIM OF STUDY

The present study was undertaken to evaluate synergistic nourishing 'Yin' effect of IG and PG from RS in vivo and in vitro through their immunoregulation and antioxidant activities.

MATERIALS AND METHODS

In this study, IG and PG fractions in RS were isolated and identified by High Performance Liquid Chromatography coupled with tandem quadrupole time-of-flight Mass Spectrometry (HPLC-Q-TOF-MS). The synergistic nourishing 'Yin' effect of two fractions were investigated in vivo and in vitro with thyroxine-induced 'Yin' deficiency (YD) mice model and primary splenic lymphocyte, respectively. The exterior syndrome signs and serologic and cellular biomarkers changes were detected. Then, the synergistic coefficient (SC) of IG and PG on every pharmacodynamics index were calculated by Webb method.

RESULTS

Compared with model and mono-therapy group (IG or PG group), IG combined with PG group significantly ameliorated YD by exerting immunoregulation and antioxidant effects. Based on the SC, IG and PG possessed a synergistic effect on heart rate, average speed, upright times, spleen index, LPO, SOD, IL-6, Na⁺-K⁺-ATP enzyme in vivo, and cAMP/cGMP, IFN-γ/IL-10, and MDA in vitro with SC > 1.

CONCLUSIONS

The nourishing 'Yin' benefits were clearly produced when IG and PG were used in combination, which provided the scientific evidence of multiple-components and multiple-approach synergistic effect of Chinese traditional herbal medicine to control and management of diseases.

The role of fish oil in attenuating cardiac oxidative stress, inflammation and fibrosis in rat model of thyrotoxicosis

Hyperthyroidism is associated with cardiovascular complications. Fish oil reduces risk of cardiovascular diseases. This study aims to evaluate the impact of fish oil on myocardial oxidative stress, inflammation and fibrosis in rat model of thyrotoxicosis. Rats were randomized into four groups; control rats, fish oil treated rats (FO, 100mg omega-3/100g body weight/day), hyperthyroid rats (Hyper, i.p levothyroxine 3 mg/kg/day), and hyperthyroid rats treated with fish oil (Hyper + FO) for 8 weeks. Changes in oxidants/antioxidants, inflammatory and fibrotic markers were measured. Thyrotoxicosis increased serum endothelin-1, thiobarbituric acid reactive substances (TBARS) and reduced activities of cardiac catalase and super oxide dismutase (SOD). Cardiac fibrosis paralleled with a decrease of matrix metalloproteinase -2 (MMP2) levels were observed in Hyper group. Use of FO increased activities of SOD and catalase, increased TBARS levels, and attenuated cardiac fibrosis by normalizing MMP-2 levels. Use of FO may attenuate cardiac oxidative stress and fibrosis in hyperthyroid states.

Deficiency of type 2 iodothyronine deiodinase reduces necroptosis activity and oxidative stress responses in retinas of Leber congenital amaurosis model mice

Thyroid hormone (TH) signaling has been shown to regulate cone photoreceptor viability. Suppression of TH signaling with antithyroid drug treatment or by targeting iodothyronine deiodinases and TH receptors preserves cones in mouse models of retinal degeneration, including the Leber congenital amaurosis Rpe65-deficient mice. This work investigates the cellular mechanisms underlying how suppressing TH signaling preserves cones in Rpe65-deficient mice, using mice deficient in type 2 iodothyronine deiodinase (Dio2), the enzyme that converts the prohormone thyroxine to the active hormone triiodothyronine (T3). Deficiency of Dio2 improved cone survival and function in Rpe65-/- and Rpe65-deficiency on a cone dominant background ( Rpe65-/-/ Nrl-/-) mice. Analysis of cell death pathways revealed that receptor-interacting serine/threonine-protein kinase (RIPK)/necroptosis activity was increased in Rpe65-/-/ Nrl-/- retinas, and Dio2 deficiency reversed the alterations. Cell-stress analysis showed that the cellular oxidative stress responses were increased in Rpe65-/-/ Nrl-/- retinas, and Dio2 deficiency abolished the elevations. Similarly, antithyroid drug treatment resulted in reduced RIPK/necroptosis activity and oxidative stress responses in Rpe65-/-/ Nrl-/- retinas. Moreover, treatment with T3 significantly induced RIPK/necroptosis activity and oxidative stress responses in the retina. This work shows that suppression of TH signaling reduces cellular RIPK/necroptosis activity and oxidative stress responses in degenerating retinas, suggesting a mechanism underlying the observed cone preservation.-Yang, F., Ma, H., Butler, M. R., Ding, X.-Q. Deficiency of type 2 iodothyronine deiodinase reduces necroptosis activity and oxidative stress responses in retinas of Leber congenital amaurosis model mice.

No copper supplementation in a corn-soybean basal diet has no adverse effects on late-phase laying hens under normal and cyclic high temperatures

Over supplementation of copper (Cu) in animal diets may cause serious pollution in soil, water and harvested crops. To minimize the potential pollution, the effects of corn-soybean basal diet with or without supplementation of 8 mg Cu/kg on laying performance, plasma biochemical metabolic indices, and antioxidant status in laying hens were evaluated under normal and cyclic high temperatures. A total of 240 Hy-Line Brown laying hens were randomly allotted to 4 treatments with 6 replicates of 10 hens per replicate according to factorial design involved in 2 temperatures [normal temperature (NT) vs. cyclic high temperature (CHT)] and 2 dietary Cu addition amount [Cu0 (0 mg/kg) vs. Cu8 (8 mg/kg in the form of CuSO4·5H2O)]. The experimental period included 1-week adaptation, 2-week heat stress and 2-week convalescence. The temperatures of NT groups in the same period or any groups during other periods were kept at 26 ± 2°C except that of CHT groups were 26 ± 2°C∼33 ± 2°C cyclically during heat stress period. CHT groups increased (P < 0.05) the rectal temperature and plasma glucose content under heat stress, but decreased (P < 0.01) the egg yield at the second week of heat stress and the first week of convalescence, and the plasma triglyceride, uric acid, and triiodothyronine levels under heat stress. Cu8 groups increased (P < 0.05) egg weight at the first week of convalescence, and plasma thyroxin level during the whole convalescence. Interactions between temperature and Cu content existed (P < 0.05) in the laying rate at the first week of convalescence, and the plasma lactic dehydrogenase level under heat stress. Conclusively, the CHT impaired laying performance. The Cu content (10.3 mg/kg) in corn-soybean basal diet might be sufficient for meeting the maintenance and production requirements of late-phase laying hens, and no Cu supplementation had no adverse effects on egg production and antioxidant indices under cyclic high (26 ± 2°C∼33 ± 2°C) or normal (26 ± 2°C) temperatures.

Cardiac ischemia/reperfusion injury is inversely affected by thyroid hormones excess or deficiency in male Wistar rats

AIM

Thyroid dysfunctions can increase the risk of myocardial ischemia and infarction. However, the repercussions on cardiac ischemia/reperfusion (IR) injury remain unclear so far. We report here the effects of hypothyroidism and thyrotoxicosis in the susceptibility to IR injury in isolated rat hearts compared to euthyroid condition and the potential role of antioxidant enzymes.

METHODS

Hypothyroidism and thyrotoxicosis were induced by administration of methimazole (MMZ, 300 mg/L) and thyroxine (T4, 12 mg/L), respectively in drinking water for 35 days. Isolated hearts were submitted to IR and evaluated for mechanical dysfunctions and infarct size. Superoxide dismutase types 1 and 2 (SOD1 and SOD2), glutathione peroxidase types 1 and 3 (GPX 1 and GPX3) and catalase mRNA levels were assessed by quantitative RT-PCR to investigate the potential role of antioxidant enzymes.

RESULTS

Thyrotoxicosis elicited cardiac hypertrophy and increased baseline mechanical performance, including increased left ventricle (LV) systolic pressure, LV developed pressure and derivatives of pressure (dP/dt), whereas in hypothyroid hearts exhibited decreased dP/dt. Post-ischemic recovery of LV end-diastolic pressure (LVEDP), LVDP and dP/dt was impaired in thyrotoxic rat hearts, whereas hypothyroid hearts exhibited improved LVEDP and decreased infarct size. Catalase expression was decreased by thyrotoxicosis.

CONCLUSION

Thyrotoxicosis was correlated, at least in part, to cardiac remodeling and increased susceptibility to IR injury possibly due to down-regulation of antioxidant enzymes, whereas hypothyroid hearts were less vulnerable to IR injury.

Myocardial Layer-Specific Strain Analysis in Children with Mitochondrial Disease

PURPOSE

Children with mitochondrial disease (MD) have clinical phenotypes that are more severe than those found in adults. In this study, we assessed cardiac function in children with MD using conventional and advanced echocardiographic measurements, explored any unique patterns present, and investigated the development of early cardiomyopathy (CMP).

MATERIALS AND METHODS

We retrospectively reviewed the medical records of 33 children with MD. All patients underwent transthoracic echocardiography with conventional and advanced myocardial analysis. We compared all data between patients and an age-matched healthy control group.

RESULTS

Conventional echocardiographic diastolic measurements of mitral E, E/A, and tissue Doppler E' were significantly lower and E/E' was significantly higher in children with MD, compared with the measurements from the control group. There was no significant difference in longitudinal and radial strain between the groups. Circumferential strain in the endocardium (p=0.161), middle myocardium (p=0.008), and epicardium (p=0.042) were lower in patients, compared to the values in controls. Circumferential strain was correlated with E' (p<0.01, r>0.60).

CONCLUSION

In children with MD, myocardial circumferential strain may develop early in all three layers, even with normally preserved longitudinal and radial strain. This may be an early diagnostic indicator with which to predict CMP in this patient population.

Zinc Ameliorate Oxidative Stress and Hormonal Disturbance Induced by Methomyl, Abamectin, and Their Mixture in Male Rats

Exposure to mixtures of toxicants (e.g., pesticides) is common in real life and a subject of current concern. The present investigation was undertaken to assess some toxicological effects in male rats following exposure to methomyl (MET), abamectin (ABM), and their combination (MET+ABM), and to evaluate the ameliorative effect of zinc co-administration. Three groups of rats were designated for MET, ABM, and the mixture treatments. Three other groups were designated for zinc in conjunction with the pesticides. Additionally, one group received water only (control), and the other represented a positive zinc treatment. The obtained results revealed that MET was acutely more toxic than ABM. The tested pesticides induced significant elevation in lipid peroxidation and catalase levels, while declined the levels of the other tested parameters e.g., Superoxide dismutase (SOD), Glutathione-S-transferase (GST), Glutathione peroxidase (GPx), Glutathione reductase (GR), Cytochrome P₄₅₀ (CYP₄₅₀), testosterone, and thyroxine). Biochemical alterations induced by the mixture were greater than those recorded for each of the individual insecticides. The joint action analysis, based on the obtained biochemical data, revealed the dominance of antagonistic action among MET and ABM. Zinc supplementation achieved noticeable ameliorative effects. It was concluded that zinc may act as a powerful antioxidant, especially in individuals who are occupationally exposed daily to low doses of such pesticides.

Contribution of Brain Tissue Oxidative Damage in Hypothyroidism-associated Learning and Memory Impairments

The brain is a critical target organ for thyroid hormones, and modifications in memory and cognition happen with thyroid dysfunction. The exact mechanisms underlying learning and memory impairments due to hypothyroidism have not been understood yet. Therefore, this review was aimed to compress the results of previous studies which have examined the contribution of brain tissues oxidative damage in hypothyroidism-associated learning and memory impairments.

Thyroid hormones in extreme longevity

The aim of the present review was to summarize knowledge about thyroid hormones (THs) and longevity. Longevity is a complex multifactorial phenomenon on which specific biological pathways, including hormonal networks involved in the regulation of homeostasis and survival, exert a strong impact. THs are the key responsible for growth, metabolism rate and energy expenditure, and help in maintaining cognition, bone and cardiovascular health. THs production and metabolism are fine tuned, and may help the organism to cope with a variety of environmental challenges. Experimental evidence suggests that hypothyroid state may favor longevity by reducing metabolism rate, oxidative stress and cell senescence. Data from human studies involving healthy subjects and centenarians seem to confirm this view, but THs changes observed in older patients affected by chronic diseases cannot be always interpreted as a protective adaptive mechanism aimed at reducing catabolism and prolonging survival. Medications, selected chronic diseases and multi-morbidity can interfere with thyroid function, and their impact is still to be elucidated.

Perinatal hypothyroidism modulates antioxidant defence status in the developing rat liver and heart

In the present study, we investigated oxidative stress parameters and antioxidant defence status in perinatal hypothyroid rat liver and heart. We found that the proteincarbonyl content did not differ significantly between the three groups both in the pup liver and in the heart. The OH˙ level was significantly decreased in the hypothyroid heart but not in the liver compared with controls. A slight but not significant decrease in SOD activity was observed in both perinatal hypothyroid liver and heart. A significantly increased activity of CAT was observed in the liver but not in the heart of hypothyroid pups. The GPx activity was considerably increased compared with controls in the perinatal hypothyroid heart and was unaltered in the liver of hypothyroid pups. We also found that vitamin E levels in the liver decreased significantly in hypothyroidism and were unaltered in the heart of perinatal hypothyroid rats. The GSH content was elevated significantly in both hypothyroid liver and heart. The total antioxidant capacity was higher in the liver of the hypothyroid group but not in the hypothyroid heart. Thyroxine replacement could not repair the above changes to normal. In conclusion, perinatal hypothyroidism modulates the oxidative stress status of the perinatal liver and heart.

Thyroid Hormones and Oxidative Stress

Thyroid hormones have a pro-oxidant effect and cause increased lipid peroxidation. Lipid peroxidation is an extremely damaging process implicated in many diseases and could be a causative factor, responsible for the varied systemic manifestations of hyperthyroidism, like myopathy and myocardial insufficiency. The activities of antioxidant scavenging enzymes like erythrocyte superoxide dismutase, catalase, and glutathione peroxidase, which prevent lipid peroxidation, are also significantly affected by hyperthyroidism and hypothyroidism. Further, it has been observed in various studies that hypothyroidism does induce changes in free radical scavenging enzymes opposite to those observed in hyperthyroidism. Oxidative injury, therefore, is an important mechanism in the pathophysiology of hyperthyroidism.

How to cite this article

Kesar V. Thyroid Hormones and Oxidative Stress. Indian J Med Biochem 2017;21(1):58-61.

Melatonin alleviates hyperthyroidism induced oxidative stress and neuronal cell death in hippocampus of aged female golden hamster, Mesocricetus auratus

Oxidative stress is a well known phenomenon under hyperthyroid condition that induces various physiological and neural problems with a higher prevalence in females. We, therefore investigated the antioxidant potential of melatonin (Mel) on hyperthyroidism-induced oxidative stress and neuronal cell death in the hippocampus region of brain (cognition and memory centre) of aged female golden hamster, Mesocricetus auratus. Aged female hamsters were randomly divided into four experimental groups (n=7); group-I: control, group-II: Melatonin (5mgkg(-1)day(-1), i.p., for one week), group-III: Hyperthyroid (100μg kg(-1)day(-1), i.p., for two weeks) and group-IV- Hyper+Mel. Hormonal profiles (thyroid and melatonin), activity of antioxidant enzymes (SOD, CAT and GPX), lipid peroxidation level (TBARS) and the specific apoptotic markers (Bax/Bcl-2 ratio and Caspase-3) expression were evaluated. A significant increase in the profile of total thyroid hormone (tT3 and tT4) in hyperthyroidic group as compared to control while tT3 significantly decreased in melatonin treated hyperthyroidic group. However, Mel level significantly decreased in hyperthyroidic group but increased in melatonin treated hyperthyroidic group. Further, the number of immune-positive cells for thyroid hormone receptor-alpha (TR-α) decreased in the hippocampus of hyperthyroidic group and increased in melatonin treated hyperthyroidic group. Profiles of antioxidant enzymes showed a significant decrease in hyperthyroidic group with a simultaneous increase in lipid peroxidation (TBARS). Melatonin treatment to hyperthyroidic group lead to decreased TBARS level with a concomitant increase in antioxidant enzyme activity. Moreover, increased expression of Bax/Bcl-2 ratio and Caspase-3, in hyperthyroidic group had elevated neuronal cell death in hippocampal area and melatonin treatment reduced its expression in hyperthyroidic group. Our findings thus indicate that melatonin reduced the hyperthyroidism-induced oxidative stress and neuronal cell death in the hippocampus region of brain, suggesting a novel therapeutic approach of melatonin for management of cognition and memory function in females under hyperthyroid condition.

The Effect of Experimental Thyroid Dysfunction on Markers of Oxidative Stress in Rat Pancreas

Preclinical Research The aim of the present study was to evaluate the effects of thyroid dysfunction on markers of oxidative stress in rat pancreas. Hypothyroidism and hyperthyroidism were, respectively, induced in rats via administration of propylthiouracil (PTU) and L-thyroxine sodium salt in drinking water for 45 days. The activities of superoxide dismutase (SOD), catalase (CAT), glutathioen peroxidase (GPx), glutathione reductase (GR), glucose-6-phosphate dehydrogenase (G6PD), xanthine oxidase (XO), and nonenzymatic markers of oxidative stress including malondialdehyde (MDA), protein carbonyl (PC), reduced glutathione (GSH), and total thiols (T-SH) were determined in the rat pancreas. In hyperthyroid rats, pancreatic CAT, SOD, GPx, GR, XO, G6PD activities were increased compared with those in hypothyroid and control groups. There were no differences in activities of antioxidant enzymes between hypothyroid and control rats. Pancreatic MDA and PC in hyperthyroid rats increased compared with hypothyroid and the control animals. Whereas, hyperthyroid rats had decreased levels of tissue GSH and T-SH compared with hypothyroid and the control groups. The findings showed that only GSH level has decreased significantly in the hypothyroid group compared with control groups. In conclusion, our results showed that experimental hyperthyroidism induces oxidative stress in pancreas of rats, but hypothyroidism has no major impact on oxidative stress markers. Drug Dev Res 77 : 199-205, 2016.   © 2016 Wiley Periodicals, Inc.

Thyroid Hormones, Oxidative Stress, and Inflammation

Inflammation and oxidative stress (OS) are closely related processes, as well exemplified in obesity and cardiovascular diseases. OS is also related to hormonal derangement in a reciprocal way. Among the various hormonal influences that operate on the antioxidant balance, thyroid hormones play particularly important roles, since both hyperthyroidism and hypothyroidism have been shown to be associated with OS in animals and humans. In this context, the nonthyroidal illness syndrome (NTIS) that typically manifests as reduced conversion of thyroxine (T₄) to triiodothyronine (T₃) in different acute and chronic systemic conditions is still a debated topic. The pathophysiological mechanisms of this syndrome are reviewed, together with the roles of deiodinases, the enzymes responsible for the conversion of T₄ to T₃, in both physiological and pathological situations. The presence of OS indexes in NTIS supports the hypothesis that it represents a condition of hypothyroidism at the tissue level and not only an adaptive mechanism to diseases.

Protective effects of 5,7,4'-trihydroxy-6,3'dimethoxy-flavone 5-O-α-l-rhamnopyranoside, isolated from Annona squamosa leaves in thyrotoxicosis and in hepatic lipid peroxidation in rats

Hitherto unknown protective effects of 5,7,4'-trihydroxy-6,3'dimethoxy-flavone 5-O-α-l-rhamnopyranoside (THDMF-Rha); isolated from Annona squamosa leaves were evaluated in l-thyroxine (l-T4)-induced thyrotoxicosis in rats. Administration of l-T4 at 500μg/kg body weight for 12days increased the levels of serum thyroid hormones, the activity of 5'-monodeiodinase-I (5'DI) and hepatic glucose-6-phosphatase (G-6Pase) as well as lipid peroxidation (LPO); with a parallel decrease in the levels of cellular antioxidants and serum lipids. However, administration of the isolated THDMF-Rha at a pre-standardized dose for 15days ameliorated the l-T4-induced alterations in the levels of thyroid hormones, hepatic LPO, G-6-Pase, 5'DI activity, and cellular levels of antioxidants and improved the status of different serum lipids, suggesting its antithyroidal and antioxidative potential. As compared to standard antithyroid drug, propylthiouracil, THDMF-Rha appeared to be more promising.

Effects of environmental temperature and dietary manganese on egg production performance, egg quality, and some plasma biochemical traits of broiler breeders

An experiment was conducted to investigate the effects of environmental temperature and dietary Mn on egg production performance, egg quality, and some plasma biochemical traits of broiler breeders. A completely randomized factorial design involved 2 environmental temperatures (a normal temperature, 21 ± 1°C, and a high temperature, 32 ± 1°C) × 3 dietary Mn treatments (a Mn-unsupplemented corn–soybean meal basal diet or the basal diet supplemented with 120 mg of Mn/kg of diet as either MnSO4·H2O or manganese proteinate). There were 6 treatments with 6 replicates (4 birds per replicate). High temperature decreased egg weight (P < 0.0001), laying rate (P < 0.0001), egg yield (P < 0.0001), feed intake (P < 0.0001), egg:feed ratio (P < 0.0001), eggshell strength (P < 0.05) and thickness (P < 0.0001), plasma triiodothyronine level (P < 0.05), and alkaline phosphatase activity (P < 0.04) whereas it increased rectal temperature (P < 0.0001); plasma malondialdehyde level (P < 0.02); and activities (P < 0.002) of lactic dehydrogenase, aspartate aminotransferase, and creatine kinase. Broiler breeders fed the diets supplemented with Mn regardless of source had greater (P < 0.05) eggshell strength and lower (P ≤ 0.05) plasma triiodothyronine level and protein carbonyl content than those fed the control diet. The broiler breeders fed the diet supplemented with the organic Mn had greater (P < 0.01) eggshell thickness than those fed the control diet. There were interactions (P < 0.05) between environmental temperature and dietary Mn in laying rate, egg yield, feed intake, and egg:feed ratio. Under normal temperature, dietary Mn did not affect the above 4 parameters; however, under high temperature, broiler breeders fed the diet supplemented with the organic Mn showed greater (P < 0.03) improvements in these 4 parameters than those fed the control diet. The results from this study indicated that high temperature significantly impaired egg production performance and eggshell quality and induced lipid peroxidation and tissue damage whereas dietary supplementation of either organic or inorganic Mn improved eggshell strength and thermotolerance and reduced protein oxidation and that the organic Mn could alleviate the negative effect of high temperature on egg production performance of broiler breeders at the period of 32 to 45 wk of age.

Role of Oxidative Stress in Thyroid Hormone-Induced Cardiomyocyte Hypertrophy and Associated Cardiac Dysfunction: An Undisclosed Story

Cardiac hypertrophy is the most documented cardiomyopathy following hyperthyroidism in experimental animals. Thyroid hormone-induced cardiac hypertrophy is described as a relative ventricular hypertrophy that encompasses the whole heart and is linked with contractile abnormalities in both right and left ventricles. The increase in oxidative stress that takes place in experimental hyperthyroidism proposes that reactive oxygen species are key players in the cardiomyopathy frequently reported in this endocrine disorder. The goal of this review is to shed light on the effects of thyroid hormones on the development of oxidative stress in the heart along with the subsequent cellular and molecular changes. In particular, we will review the role of thyroid hormone-induced oxidative stress in the development of cardiomyocyte hypertrophy and associated cardiac dysfunction, as well as the potential effectiveness of antioxidant treatments in attenuating these hyperthyroidism-induced abnormalities in experimental animal models.

Differential involvement of various sources of reactive oxygen species in thyroxin-induced hemodynamic changes and contractile dysfunction of the heart and diaphragm muscles

Thyroid hormones are key regulators of basal metabolic state and oxidative metabolism. Hyperthyroidism has been reported to cause significant alterations in hemodynamics, and in cardiac and diaphragm muscle functions, all of which have been linked to increased oxidative stress. However, the definite source of increased reactive oxygen species (ROS) in each of these phenotypes is still unknown. The goal of the current study was to test the hypothesis that thyroxin (T4) may produce distinct hemodynamic, cardiac, and diaphragm muscle abnormalities by differentially affecting various sources of ROS. Wild-type and T4 mice with and without 2-week treatments with allopurinol (xanthine oxidase inhibitor), apocynin (NADPH oxidase inhibitor), L-NIO (nitric oxide synthase inhibitor), or MitoTEMPO (mitochondria-targeted antioxidant) were studied. Blood pressure and echocardiography were noninvasively evaluated, followed by ex vivo assessments of isolated heart and diaphragm muscle functions. Treatment with L-NIO attenuated the T4-induced hypertension in mice. However, apocynin improved the left-ventricular (LV) dysfunction without preventing the cardiac hypertrophy in these mice. Both allopurinol and MitoTEMPO reduced the T4-induced fatigability of the diaphragm muscles. In conclusion, we show here for the first time that T4 exerts differential effects on various sources of ROS to induce distinct cardiovascular and skeletal muscle phenotypes. Additionally, we find that T4-induced LV dysfunction is independent of cardiac hypertrophy and NADPH oxidase is a key player in this process. Furthermore, we prove the significance of both xanthine oxidase and mitochondrial ROS pathways in T4-induced fatigability of diaphragm muscles. Finally, we confirm the importance of the nitric oxide pathway in T4-induced hypertension.

Efeito da coenzima Q10 nos danos oxidativos induzidos pela L-tiroxina no músculo sóleo de ratos

INTRODUÇÃO: os músculoesqueléticos são tecidos dinâmicos que podem alterar suas características fenotípicas proporcionando melhor adaptação funcional com estímulos variados. A L-tiroxina é um hormônio produzido pela glândula tireoide e tem sido utilizada como modelo experimental para estimulação de estresse oxidativo no músculo esquelético. A coenzima Q10 é uma provitamina lipossolúvel sintetizada endogenamente e naturalmente encontrada em alimentos como carne vermelha, peixes, cereais, brócolis e espinafre. Apresenta propriedade antioxidante e tem potencial no tratamento de doenças degenerativas e neuromusculares.OBJETIVO: avaliar o efeito protetor da coenzima Q10 no músculo sóleo de ratos frente aos danos oxidativos provocados pela L-tiroxina.MÉTODOS: os ratos foram distribuídos em quatro grupos de seis animais cada: Grupo 1 controle; Grupo 2 coenzima Q10; Grupo 3 L-tiroxina e Grupo 4 coenzima Q10 e L-tiroxina. Após a eutanásia, o sangue dos animais foi colhido e foi analisada a atividade sérica das enzimas creatina quinase CK e aspartato aminotransferase AST. No homogenato do músculo sóleo foram avaliados fatores relacionados ao estresse oxidativo.RESULTADOS: a coenzima Q10 protegeu o músculo sóleo dos danos provocados pela L-tiroxina e favoreceu a manutenção da atividade das enzimas antioxidantes glutationa redutase e glutationa peroxidase, da concentração de glutationa reduzida e oxidada, além de evitar a lipoperoxidação.CONCLUSÃO: os resultados indicam que a coenzima Q10 protege o músculo sóleo de ratos dos danos oxidativos provocados pela L-tiroxina.

Evaluation of the Relationship Between Ischemia-Modified Albumin Levels and Thyroid Hormone Levels

BACKGROUND

A novel ischemia marker named ischemia modified albumin was previously considered as an early marker of myocardial ischemia, however due to recent reports, its contribution was demonstrated in different pathologies such as oxidative stress, diabetes, stroke and cancer. We aimed to investigate the relation between oxidative stress and thyroid dysfunctions determining IMA levels since IMA is closely related with increased oxidative stress.

METHODS

A total of 88 individuals were participated in this study: 34 cases in hypothyroid, 27 cases in hyperthyroid and 27 cases in euthyroid group. Ischemia-modified albumin levels were measured by albumin cobalt binding test and thyroid hormone levels were determined with electrochemiluminescent method.

RESULTS

Ischemia modified albumin levels were significantly decreased in hypothyroid group compared to hyperthyroid and euthyroid groups (p < 0.001). In hyperthyroid individuals ischemia modified albumin levels were higher compared to euthyroid ones (p < 0.001). Ischemia modified albumin was negatively correlated with TSH levels (r = -0.473, p < 0.001), and positively correlated with FT4 and FT3 levels (r = 0.496, p < 0.001 and r = 0.275, p = 0.010, respectively).

CONCLUSION

We suggest that albumin adjusted IMA levels are significantly lower in hypothyroid group than hyperthyroid and euthyroid groups.

Supplementation of T3 recovers hypothyroid rat liver cells from oxidatively damaged inner mitochondrial membrane leading to apoptosis

Hypothyroidism is a growing medical concern. There are conflicting reports regarding the mechanism of oxidative stress in hypothyroidism. Mitochondrial oxidative stress is pivotal to thyroid dysfunction. The present study aimed to delineate the effects of hepatic inner mitochondrial membrane dysfunction as a consequence of 6-n-propyl-2-thiouracil-induced hypothyroidism in rats. Increased oxidative stress predominance in the submitochondrial particles (SMP) and altered antioxidant defenses in the mitochondrial matrix fraction correlated with hepatocyte apoptosis. In order to check whether the effects caused by hypothyroidism are reversed by T₃, the above parameters were evaluated in a subset of T₃-treated hypothyroid rats. Complex I activity was inhibited in hypothyroid SMP, whereas T₃ supplementation upregulated electron transport chain complexes. Higher mitochondrial H₂O₂ levels in hypothyroidism due to reduced matrix GPx activity culminated in severe oxidative damage to membrane lipids. SMP and matrix proteins were stabilised in hypothyroidism but exhibited increased carbonylation after T₃ administration. Glutathione content was higher in both. Hepatocyte apoptosis was evident in hypothyroid liver sections; T₃ administration, on the other hand, exerted antiapoptotic and proproliferative effects. Hence, thyroid hormone level critically regulates functional integrity of hepatic mitochondria; hypothyroidism injures mitochondrial membrane lipids leading to hepatocyte apoptosis, which is substantially recovered upon T₃ supplementation.

Thyroid status affects membranes susceptibility to free radicals and oxidative balance in skeletal muscle of Muscovy ducklings (Cairina moschata)

Thyroid hormones (TH) are major contributor to oxidative stress in mammals because they (1) stimulate reactive oxygen species generation (ROS), (2) impair antioxidant defenses, and (3) increase the susceptibility to free radicals of most tissues. Unlike mammals, THs seem to diminish mitochondrial ROS while they have limited effect on the antioxidant machinery in birds. However, how THs modify the susceptibility to ROS has never been explored in an avian model, and very little is known about their effect on oxidative balance in birds. Therefore, the objective of our study was to examine the effect of chronic pharmacological hypo- and hyperthyroidism on (i) the susceptibility of mitochondrial membranes to ROS; and (ii) the level of oxidative stress assessed by measuring oxidative damage to lipids, nucleic acids and proteins in the gastrocnemius muscle of ducklings. We show that hypothyroidism had no effect on the susceptibility of mitochondrial membranes to free radicals. Hypothyroid ducklings had lower oxidized lipids (-31%) and DNA (-25%) but a similar level of protein carbonylation relative to controls. Conversely, mitochondrial membranes of hyperthyroid ducklings exhibited higher unsaturation (+12%) and peroxidation (+31%) indexes than in controls indicating a greater susceptibility to free radicals. However, hyperthyroid ducklings exhibited more oxidative damages on proteins (+67%) only, whereas lipid damages remained unchanged, and there was a slight reduction (-15%) in damages to DNA compared to euthyroid controls. Our results indicate that birds and mammals present fundamental differences in their oxidative stress response to thyroid status.

Hypothyroidism alters antioxidant defence system in rat brainstem during postnatal development and adulthood

The present investigation was carried out to evaluate alterations in oxidative stress parameter [lipid peroxidation (LPx)] and antioxidant enzyme activities [superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx)] in rat brainstem in response to neonatal hypothyroidism during development (from birth to 7, 15 and 30 days old) and adulthood (90 days old). Hypothyroidism in rats was induced by feeding the lactating mothers (from the day of parturition till weaning, 25 days old) or directly to the pups with 0.05 % [6-n-propyl 2-thiouracil (PTU)] in drinking water. Increased level of LPx was observed in brainstem of 7 days old hypothyroid rats, accompanied by augmented activities of SOD and GPx. In 15 and 30 days old hypothyroid rat brainstem, a significant decline in LPx was observed. Significantly increased activities of CAT and GPx were observed in 15 and 30 days PTU-treated rats. Decreased level of LPx was observed in brainstem of rats treated with PTU from birth to 30 days followed by withdrawal up to 90 days of age (transient hypothyroidism) as compared to control and persistent treatment of PTU up to 90 days of age. Activities of CAT and GPx were decreased in persistent hypothyroid rats of 90 days old with respect to control and transient hypothyroid rats. On the other hand, SOD activity was decreased in both persistent and transient hypothyroid rats with respect to control rats. These results suggest that the PTU-induced neonatal hypothyroidism modulates the antioxidant defence system during postnatal development and adulthood in brainstem of rats.

[The activity of glutathione antioxidant system at melaksen and valdoxan action under experimental hyperthyroidism in rats]

Investigation of glutathione antioxidant system activity and diene conjugates content in rats liver and blood serum at the influence of melaksen and valdoxan under experimental hyperthyroidism (EG) has been revealed. It has been established that the activities of glutathione reductase (GR), glutathione peroxidase (GP) and glutathione transferase (GT), growing at pathological conditions, change to the side of control value at these substunces introduction. Reduced glutathione content (GSH) at melaxen and valdoxan action increased compared with values under the pathology, that, obviously, could be associated with a reduction of its spending on the detoxication of free radical oxidation (FRO) toxic products. Diene conjugates level in rats liver and blood serum, increasing at experimental hyperthyroidism conditions, under introduction of melatonin level correcting drugs, also approached to the control meaning. Results of the study indicate on positive effect of melaxen and valdoxan on free radical homeostasis, that appears to be accompanied by decrease of load on the glutathione antioxidant system in comparison with the pathology.

Thyroid hormones and antioxidant systems: focus on oxidative stress in cardiovascular and pulmonary diseases

In previous works we demonstrated an inverse correlation between plasma Coenzyme Q₁₀ (CoQ₁₀) and thyroid hormones; in fact, CoQ₁₀ levels in hyperthyroid patients were found among the lowest detected in human diseases. On the contrary, CoQ₁₀ is elevated in hypothyroid subjects, also in subclinical conditions, suggesting the usefulness of this index in assessing metabolic status in thyroid disorders. A Low-T3 syndrome is a condition observed in several chronic diseases: it is considered an adaptation mechanism, where there is a reduction in pro-hormone T4 conversion. Low T3-Syndrome is not usually considered to be corrected with replacement therapy. We review the role of thyroid hormones in regulation of antioxidant systems, also presenting data on total antioxidant capacity and Coenzyme Q₁₀. Published studies suggest that oxidative stress could be involved in the clinical course of different heart diseases; our data could support the rationale of replacement therapy in low-T3 conditions.

The role of thyroid hormones as inductors of oxidative stress and neurodegeneration

Reactive oxygen species (ROS) are oxidizing agents amply implicated in tissue damage. ROS production is inevitably linked to ATP synthesis in most cells, and the rate of production is related to the rate of cell respiration. Multiple antioxidant mechanisms limit ROS dispersion and interaction with cell components, but, when the balance between ROS production and scavenging is lost, oxidative damage develops. Many traits of aging are related to oxidative damage by ROS, including neurodegenerative diseases. Thyroid hormones (THs) are a major factor controlling metabolic and respiratory rates in virtually all cell types in mammals. The general metabolic effect of THs is a relative acceleration of the basal metabolism that includes an increase of the rate of both catabolic and anabolic reactions. THs are related to oxidative stress not only by their stimulation of metabolism but also by their effects on antioxidant mechanisms. Thyroid dysfunction increases with age, so changes in THs levels in the elderly could be a factor affecting the development of neurodegenerative diseases. However, the relationship is not always clear. In this review, we analyze the participation of thyroid hormones on ROS production and oxidative stress, and the way the changes in thyroid status in aging are involved in neurodegenerative diseases.

The NO/ONOO-cycle as the central cause of heart failure

The NO/ONOO-cycle is a primarily local, biochemical vicious cycle mechanism, centered on elevated peroxynitrite and oxidative stress, but also involving 10 additional elements: NF-κB, inflammatory cytokines, iNOS, nitric oxide (NO), superoxide, mitochondrial dysfunction (lowered energy charge, ATP), NMDA activity, intracellular Ca(2+), TRP receptors and tetrahydrobiopterin depletion. All 12 of these elements have causal roles in heart failure (HF) and each is linked through a total of 87 studies to specific correlates of HF. Two apparent causal factors of HF, RhoA and endothelin-1, each act as tissue-limited cycle elements. Nineteen stressors that initiate cases of HF, each act to raise multiple cycle elements, potentially initiating the cycle in this way. Different types of HF, left vs. right ventricular HF, with or without arrhythmia, etc., may differ from one another in the regions of the myocardium most impacted by the cycle. None of the elements of the cycle or the mechanisms linking them are original, but they collectively produce the robust nature of the NO/ONOO-cycle which creates a major challenge for treatment of HF or other proposed NO/ONOO-cycle diseases. Elevated peroxynitrite/NO ratio and consequent oxidative stress are essential to both HF and the NO/ONOO-cycle.