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

Pancreatic inflammation induced by hypothyroidism in female rabbits is associated with cholesterol accumulation and a reduced expression of CYP51A1, FXRβ, and PPARβ/δ

In women and animal models, hypothyroidism induces hypercholesterolemia, pancreatitis, and insulitis. We investigated whether lipids are involved in the effects of hypothyroidism in the pancreas. Control (n = 6) and hypothyroid (n = 6) adult female rabbits were used. We quantified serum and pancreatic triacylglycerol and total cholesterol levels, the oxidative and antioxidant status, and the expression of low-density lipoprotein cholesterol receptor (LDLR) in the pancreas. Inflammation of the pancreas was evaluated by infiltration of immune cells positive to CD163 and α-farnesoid receptor (FXRα). Other lipid players involved in both inflammation and insulin secretion of the pancreas, such as lanosterol 14-α-demethylase (CYP51A1), β-farnesoid receptor (FXRβ), 3β-hydroxysteroid dehydrogenase (3β-HSD), and peroxisome proliferator-activated receptor β (PPARβ/δ), were quantified. Groups were compared by t-Student or U-Mann-Whitney tests (p ≤ 0.05). Hypothyroidism induced hypercholesterolemia and a high cholesterol accumulation in the pancreas of female rabbits, without affecting oxidative or antioxidative status nor the expression of LDLR. The pancreas of hypothyroid females showed inflammation identified by a great infiltration of immune cells, macrophages CD163+, and loss of expression of FXRα+ in immune cells. Moreover, a reduced expression of CYP51A1, FXRβ, and PPARβ/δ, but not 3β-HSD, in the hypothyroid pancreas was found. Pancreatitis and insulitis promoted by hypothyroidism may be related to the accumulation of cholesterol, lanosterol actions, and the activation of PPARβ/δ. All inflammatory markers evaluated in this study are related to glucose regulation, suggesting the link between hypothyroidism and diabetes.

Advancing thyroid disease research: The role and potential of zebrafish model

Thyroid disorders significantly affect human metabolism, cardiovascular function, skeletal health, and reproductive systems, presenting a complex challenge due to their multifactorial nature. Understanding the underlying mechanisms and developing novel therapeutic approaches require appropriate models. Zebrafish, with their genetic tractability, short life cycle, and physiological relevance, have emerged as a valuable model for investigating thyroid diseases. This review provides a comprehensive analysis of the zebrafish thyroid gland's structure and function, explores its application in modeling thyroid pathologies such as hypothyroidism, hyperthyroidism, and thyroid cancer, and discusses current limitations and possible improvements. Furthermore, it outlines future directions for zebrafish-based research, focusing on enhancing the model's relevance to human thyroid disease and its potential to expedite the development of clinical therapies.

Maternal hypothyroidism causes oxidative stress and endoplasmic reticulum stress in the maternal-fetal interface of rats

Maternal hypothyroidism is associated with pre-eclampsia and intrauterine growth restriction, gestational diseases involving oxidative stress (OS) and endoplasmic reticulum stress (ERS) in the placenta. However, it is not known whether hypothyroidism also causes OS and ERS at the maternal-fetal interface. The aim was to evaluate the fetal-placental development and the expression of mediators of OS and of the unfolded protein response (UPR) in the maternal-fetal interface of hypothyroid rats. Hypothyroidism was induced in Wistar rats with propylthiouracil and the fetal-placental development and placental and decidual expression of antioxidant, hypoxia, and UPR mediators were analyzed at 14 and 18 days of gestation (DG), as well the expression of 8-OHdG and MDA, and reactive oxygen species (ROS) and peroxynitrite levels. Hypothyroidism reduced fetal weight at 14 and 18 DG, in addition to increasing the percentage of fetal death and reducing the weight of the uteroplacental unit at 18 DG. At 14 DG, there was greater decidual and/or placental immunostaining of Hif1α, 8-OHdG, MDA, SOD1, GPx1/2, Grp78 and CHOP in hypothyroid rats, while there was a reduction in placental and/or decidual gene expression of Sod1, Gpx1, Atf6, Perk, Ho1, Xbp1, Grp78 and Chop in the same gestational period. At 18 DG, hypothyroidism increased the placental ROS levels and the decidual and/or placental immunostaining of HIF1α, 8-OHdG, MDA, ATF4, GRP78 and CHOP, while it reduced the immunostaining and enzymatic activity of SOD1, CAT, GST. Hypothyroidism increased the placental mRNA expression of Hifα, Nrf2, Sod2, Gpx1, Cat, Perk, Atf6 and Chop at 18 DG, while decreasing the decidual expression of Sod2, Cat and Atf6. These findings demonstrated that fetal-placental restriction in female rats with hypothyroidism is associated with hypoxia and dysregulation in placental and decidual expression of UPR mediators and antioxidant enzymes, and activation of oxidative stress and endoplasmic reticulum stress at the maternal-fetal interface.

Essentiality, relevance, and efficacy of adjuvant/combinational therapy in the management of thyroid dysfunctions

Thyroid dysfunction is the most prevalent endocrine disorder worldwide having an epidemiology of 11% in Indians, 4.6% in the United Kingdom, and 2% in the United States of America among the overall population. The common thyroid disorders include hypothyroidism, hyperthyroidism, Hashimoto's thyroiditis, and thyroid cancer. This review briefly elaborates the molecular regulation and mechanism of thyroid hormone, and its associated thyroid disorders. The thyroid hormones regulate critical biochemical functions in brain development and function. Hypothyroidism is mainly associated with dysregulation of cytokines, increased ROS production, and altered signal transduction in major regions of the brain. In addition, it is associated with reduced antioxidant capacity and increased oxidative stress in humans. Though 70% of thyroid disorders are caused by heredity, environmental factors have a significant influence in developing autoimmune thyroid disorders in people who are predisposed to them. This drives us to understand the relationship between environmental factors and thyroid dysregulated disorders. The treatment option for the thyroid disorder includes antithyroid medications, receiving radioactive iodine therapy, or surgery at a critical stage. However, antithyroid drugs are not typically used long-term in thyroid disease due to the high recurrence rate. Adjuvant treatment of antioxidants can produce better outcomes with anti-thyroid drug treatment. Thus, Adjuvant therapy has been proven as an effective strategy for managing thyroid dysfunction, herbal remedies can be used to treat thyroid dysfunction in the future, which in turn can reduce the prevalence of thyroid disorders.

Saikosaponin A-Induced Gut Microbiota Changes Attenuate Severe Acute Pancreatitis through the Activation of Keap1/Nrf2-ARE Antioxidant Signaling

Objective

Severe acute pancreatitis (SAP) is a serious and life-threatening disease associated with multiple organ failure and a high mortality rate and is accompanied by distinct oxidative stress and inflammatory responses. Saikosaponin A has strong antioxidant properties and can affect the composition of gut microbiota. We sought to determine the effects of Saikosaponin A interventions on SAP by investigating the changes of gut microbiota and related antioxidant signaling.

Methods

A SAP model was established in Sprague-Dawley (SD) rats through the injection of sodium taurocholate into the biliopancreatic duct and confirmed by elevated levels of serum lipase and amylase. The model was fed a standard diet either with saline solution or with Saikosaponin A. Fecal microbiota transplantation (FMT) from Saikosaponin A-induced rats into the rat model was performed to test the effects of gut microbiota. The composition of gut microbiota was analyzed by using 16S rRNA gene sequencing. We measured apoptotic status, inflammatory biomarkers, and Keap1-Nrf2-ARE ((Kelch-like ECH-associated protein 1) nuclear factor erythroid 2-related factor 2-antioxidant response element) antioxidant signaling.

Results

Saikosaponin A intervention attenuated SAP lesions and reduced the levels of serum amylase and lipase, oxidative stress, and inflammatory responses by reducing pathological scores and affecting the serum level of oxidative and inflammatory factors. Meanwhile, the expression of Keap1-Nrf2-ARE was increased. Saikosaponin A intervention improved microbiota composition by increasing the relative abundance of Lactobacillus and Prevotella species. FMT resulted in similar results as those caused by the Saikosaponin A intervention, suggesting Saikosaponin A may exert its function via the improvement of gut microbiota composition.

Conclusions

Saikosaponin A-induced gut microbiota changes attenuate SAP progression in the rat model and may be a potential natural drug for adjuvant treatment of SAP. Further work is needed to clear up the points.

Oxidative Stress Produced by Hyperthyroidism Status Induces the Antioxidant Enzyme Transcription through the Activation of the Nrf-2 Factor in Lymphoid Tissues of Balb/c Mice

Hyperthyroidism is an endocrine disorder characterized by excessive secretion of thyroid hormones T3 and T4. Thyroid hormones exert pleiotropic actions on numerous tissues and induce an overall increase in metabolism, with an increase in energy demand and oxygen consumption. Therefore, the purpose of this study was to investigate the effects of hyperthyroidism on the production of reactive oxygen species (ROS) in lymph node and spleen cells of euthyroid and hyperthyroid mice, analyzing antioxidant mechanisms involved in the restitution of the cellular redox state. For this, thirty female Balb/c (H-2d) mice were randomly divided into two groups: euthyroid (by treatment with placebo) and hyperthyroid (by treatment with 12 mg/l of T4 in drinking water for 30 days). We found a significant increase in ROS and an increase in the genomic and protein expression of the antioxidant enzymes catalase (CAT) and glutathione peroxidase-1 (GPx-1) in lymph node and spleen cells of hyperthyroid mice. In vitro treatment with H₂O₂ (250 μM) of the lymphoid cells of euthyroid mice increased the expression levels of CAT and GPx-1. The hyperthyroidism increased the phosphorylation levels of Nrf2 (nuclear factor erythroid 2-related factor) and the kinase activity of protein kinase C (PKC) and extracellular signal-regulated kinase (ERK). Additionally, we found an increase in the expression of the classic isoenzymes of PKCα, β and γ. In conclusion, these results indicated that the increase in ROS found in the hyperthyroid state induces the antioxidant enzyme transcription through the activation of the Nrf-2 factor in lymphoid tissues. This shows the influence of hyperthyroidism on the regulation of the cellular antioxidant system.

An early stage in T4-induced hyperthyroidism is related to systemic oxidative stress but does not influence the pentose cycle in erythrocytes and systemic inflammatory status

OBJECTIVE

Hyperthyroidism causes many injuries in its target organs and the consequences are reflected systemically. As systemic alterations in hyperthyroidism at earlier stages have received partial attention, this study aimed to investigate systemic redox and inflammatory status at an early stage of T4-induced hyperthyroidism.

MATERIALS AND METHODS

Male Wistar rats were assigned to control and hyperthyroid groups (n = 7/group). The hyperthyroid group received L-thyroxine (12 mg/L) in their drinking water for 14 days whereas control group received only the vehicle. Body weight was measured on the 1st and 14th day of the protocol. On the 14th day, animals were anaesthetized. Blood was then collected from the retro-orbital venous plexus and then the animals were euthanised. The blood was separated into plasma and erythrocytes. Plasma was used to measure ROS levels, sulfhydryl compounds, IL-10, TNF-α and LDH levels; erythrocytes were used for the analysis of thioredoxin reductase activity, glutaredoxin content, and pentose cycle enzymes (total G6PD, G6PD and 6PGD).

RESULTS

Hyperthyroid animals presented body weight gain and final body weight reduction, which was associated with increased ROS levels and decreased sulfhydryl content in plasma. Thioredoxin reductase activity, glutaredoxin content, and pentose cycle enzymes levels in erythrocytes, as well as IL-10, TNF-α and LDH plasma levels were unaltered.

CONCLUSION

Taken together, our results suggest an impairment in corporal mass associated with systemic oxidative stress at this stage of hyperthyroidism. Meanwhile, the pentose cycle was not influenced and systemic inflammation and tissue damage seem to be absent at this stage of hyperthyroidism.

Insulin resistance and diabetes in hyperthyroidism: a possible role for oxygen and nitrogen reactive species

In addition to insulin, glycemic control involves thyroid hormones. However, an excess of thyroid hormone can disturb the blood glucose equilibrium, leading to alterations of carbohydrate metabolism and, eventually, diabetes. Indeed, experimental and clinical hyperthyroidism is often accompanied by abnormal glucose tolerance. A common characteristic of hyperthyroidism and type 2 diabetes is the altered mitochondrial efficiency caused by the enhanced production of reactive oxygen and nitrogen species. It is known that an excess of thyroid hormone leads to increased oxidant production and mitochondrial oxidative damage. It can be hypothesised that these species represent the link between hyperthyroidism and development of insulin resistance and diabetes, even though direct evidence of this relationship is lacking. In this review, we examine the literature concerning the effects of insulin and thyroid hormones on glucose metabolism and discuss alterations of glucose metabolism in hyperthyroid conditions and the cellular and molecular mechanisms that may underline them.

Does hypothyroidism augment sun-induced skin damage?

OBJECTIVES

We investigated the mutual effects of overt hypothyroidism and prolonged sunlight exposure on free radical accumulation and oxidative skin damage.

METHODS

Free radical accumulation was evaluated by monitoring the transformation of 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) into MTT-formazan. The pro-oxidant enzymes xanthine oxidase (XO) and NADPH-diaphorase were measured in the skin. XO activity was estimated based on the yield of uric acid, while NADPH-diaphorase reactivity was monitored histochemically as an indirect marker of nitric oxide synthase and nitric oxide activity. Cellular damage was determined by malondialdehyde formation, a marker for lipid peroxidation.

RESULTS

In the skin of both euthyroid and hypothyroid animals, solar simulated ultraviolet irradiance increased the activity of XO and the NADPHdiaphorase reactivity as a protective response to formation of free radicals, such as reactive oxygen or nitrogen species. These pro-oxidant enzymes diminished in hypothyroid rats. Accumulation of the same amount of free radicals led to similar peroxidation in both hypothyroid and irradiated euthyroid rats. Hypothyroid skin after UV-exposure showed even greater lipid peroxidation.

DISCUSSION

The hypothyroid state could be a risk factor for enhanced oxidative skin damage in chronic photo-exposed skin due to oxidative stress. The lipid peroxidation is one of the major pathways by which photo-oxidative stress promotes photocarcinogenesis and photo-aging.

The Roles of Thyroid and Thyroid Hormone in Pancreas: Physiology and Pathology

It is widely accepted that thyroid hormones (THs), secreted from the thyroid, play important roles in energy metabolism. It is also known that THs also alter the functioning of other endocrine glands; however, their effects on pancreatic function have not yet been reviewed. One of the main functions of the pancreas is insulin secretion, which is altered in diabetes. Diabetes, therefore, could be related to thyroid dysfunction. Earlier research on this subject focused on TH regulation of pancreas function (such as insulin secretion) or on insulin function through TH-mediated increase of energy metabolism. Afterwards, epidemiological investigations and animal test research found a link between autoimmune diseases, thyroid dysfunction, and pancreas pathology; however, the underlying mechanisms remain unknown. Furthermore, recent studies have shown that THs also play important roles in pancreas development and on islet pathology, both in diabetes and in pancreatic cancer. Therefore, an overview of the effects of thyroid and THs on pancreas physiology and pathology is presented. The topics contained in this review include a summary of the relationship between autoimmune thyroid dysfunction and autoimmune pancreas lesions and the effects of THs on pancreas development and pancreas pathology (diabetes and pancreatic cancer).

Vitamin E improved redox homeostasis in heart and aorta of hypothyroid rats

OBJECTIVES

The objective of this study was to evaluate the effect of vitamin E on the oxidative stress parameters and antioxidant defense enzymes in the heart and aorta of 6-n-propylthiouracil (PTU)-induced hypothyroid rats.

METHODS

The animals were divided into 4 experimental groups: Group 1 (Euthyroid) received tap water, Group 2 (Hypothyroid) received 0.05 % of PTU in dissolved in their drinking water, Group 3 (PTU+Vit E) hypothyroid rats treated with vitamin E, and Group 4 (Euthyroid+Vit E). Vitamin E was injected daily (20 mg/kg) to groups 3 and 4 via daily gavage for 6 weeks. Malondialdehyde (MDA) levels, total thiol levels, and the activities of Cu, Zn-superoxide dismutase (SOD) and catalase (CAT) were evaluated in the aortic and cardiac tissues.

RESULTS

A significant decrease of thyroxine (T4) serum levels confirmed hypothyroidism in rats, which received PTU. The MDA level increased and total thiol level decreased in the hypothyroid group compared to control group (p<0.001). Th e activities of SOD and CAT significantly decreased in the hypothyroid rats in comparison to the control. Vitamin E treatment resulted in increased levels of total thiol, SOD, and CAT within aortic and cardiac tissues and decreased levels of MDA in comparison with the hypothyroid group (p<0.01-p<0.001).

CONCLUSIONS

PTU-induced hypothyroidism resulted in oxidative stress. Chronic administration of vitamin E to hypothyroid rats decreased the oxidative stress markers in the aortic and cardiac tissues.