Hypothyroidism in the developing rat brain is associated with marked oxidative stress and aberrant intraneuronal accumulation of neurofilaments

Perinatal thyroid hormone deficiency leads to oxidative stress-induced neuronal damage and activation of astrocytes in rat hippocampus: Neuroprotective effect of exercise

Thyroid hormones play a crucial role in proper brain development. This study examined the effects of developmental thyroid hormone deficiency on neuronal survival, glial fibrillary acidic protein (GFAP)-positive cells, and oxidative stress biomarkers in the hippocampus of congenital hypothyroid rats. The effectiveness of treadmill exercise in attenuating oxidative stress-induced neuronal damage and astrocyte activation was also evaluated. Pregnant Wistar rats in the hypothyroid group received propylthiouracil in their drinking water from gestational day 6 until weaning, while control dams received only tap water. Then, male offspring from both groups were further divided into two sub-groups: with or without four weeks of treadmill exercise. After sacrifice, the right hemispheres were processed for cresyl violet staining and immunohistochemistry, while the left hippocampi were used for biochemical assays. Results showed a reduced number of neurons and an increased number of GFAP-positive cells in the CA1 region of hypothyroid rats, with no significant changes in the CA3 region. Additionally, congenital hypothyroidism was associated with increased malondialdehyde levels, decreased glutathione levels, and reduced superoxide dismutase and catalase activity in the hippocampus. Treadmill exercise reduced astrocyte activation and protected neurons by inhibiting oxidative stress. Collectively, our results indicate that congenital thyroid hormone deficiency triggers astrocyte activation and compromises neuronal survival in the CA1 region by inducing oxidative stress. Exercise may serve as a beneficial supplementary treatment for attenuating oxidative stress-induced neuronal damage in congenital hypothyroidism.

Molecular mechanisms of neurofilament alterations and its application in assessing neurodegenerative disorders

Neurofilaments are intermediate filaments present in neurons. These provide structural support and maintain the size and shape of the neurons. Dysregulation, mutation, and aggregation of neurofilaments raise the levels of these proteins in the blood and cerebrospinal fluid (CSF), which are characteristic features of axonal damage and certain rare neurological diseases, such as Giant Axonal Neuropathy and Charcot-Mare-Tooth disease. Understanding the structure, dynamics, and function of neurofilaments has been greatly enhanced by a diverse range of biochemical and preclinical investigations conducted over more than four decades. Recently, there has been a resurgence of interest in post-translational modifications of neurofilaments, such as phosphorylation, aggregation, mutation, oxidation, etc. Over the past twenty years, several rare disorders have been studied from structural alterations of neurofilaments. These disorders are monitored by fluid biomarkers such as neurofilament light chains. Currently, there are many tools, such as Enzyme-Linked Immunosorbent Assay, Electrochemiluminescence Assay, Single-Molecule Array, Western/immunoblotting, etc., in use to assess the neurofilament proteins in Blood and CSF. However, all these techniques utilize expensive, non-specific, or antibody-based methods, which make them unsuitable for routine screening of neurodegenerative disorders. This provides room to search for newer sensitive, cost-effective, point-of-care tools for rapid screening of the disease. For a long time, the molecular mechanisms of neurofilaments have been poorly understood due to insufficient research attempts, and a deeper understanding of them remains elusive. Therefore, this review aims to highlight the available literature on molecular mechanisms of neurofilaments and the function of neurofilaments in axonal transport, axonal conduction, axonal growth, and neurofilament aggregation, respectively. Further, this review discusses the role of neurofilaments as potential biomarkers for the identification of several neurodegenerative diseases in clinical laboratory practice.

Edited magnetic resonance spectroscopy in the neonatal brain

J-difference-edited spectroscopy is a valuable approach for the detection of low-concentration metabolites with magnetic resonance spectroscopy (MRS). Currently, few edited MRS studies are performed in neonates due to suboptimal signal-to-noise ratio, relatively long acquisition times, and vulnerability to motion artifacts. Nonetheless, the technique presents an exciting opportunity in pediatric imaging research to study rapid maturational changes of neurotransmitter systems and other metabolic systems in early postnatal life. Studying these metabolic processes is vital to understanding the widespread and rapid structural and functional changes that occur in the first years of life. The overarching goal of this review is to provide an introduction to edited MRS for neonates, including the current state-of-the-art in editing methods and editable metabolites, as well as to review the current literature applying edited MRS to the neonatal brain. Existing challenges and future opportunities, including the lack of age-specific reference data, are also discussed.

Neuronal Nitric Oxide Inhibitor 7-Nitroindazole Improved Brain-Derived Neurotrophic Factor and Attenuated Brain Tissues Oxidative Damage and Learning and Memory Impairments of Hypothyroid Juvenile Rats

Hypothyroidism-associated learning and memory impairment is reported to be connected to oxidative stress and reduced levels of brain-derived neurotrophic factor (BDNF). The effects of neuronal nitric oxide inhibitor 7-nitroindazole (7NI) on brain tissues oxidative damage, nitric oxide (NO), BDNF and memory impairments in hypothyroid juvenile rats were investigated. Male Wistar juvenile rats (20 days old) were divided into five groups, including Martinez et al. (J Neurochem 78 (5):1054-1063, 2001). Control in which vehicle was injected instead of 7NI, (Jackson in Thyroid 8 (10):951-956, 1998) Propylthiouracil (PTU) where 0.05% PTU was added in drinking water and vehicle was injected instead of 7NI, (Gong et al. in BMC Neurosci 11 (1):50, 2010; Alva-Sánchez et al. in Brain Res 1271:27-35, 2009; Anaeigoudari et al. in Pharmacol Rep 68 (2): 243-249, 2016) PTU-7NI 5, PTU-7NI 10 and PTU-7NI 20 in which 5, 10, or 20 mg/kg7NI was injected intraperitoneally (i.p.). Following 6 weeks, Morris water maze (MMW) and passive avoidance learning (PAL) tests were used to evaluate the memory. Finally, the hippocampus and the cortex of the rats were removed after anesthesia by urethane to be used for future analysis. The escape latency and traveled path in MWM test was increased in PTU group (P < 0.001). PTU also reduced the latency to enter the dark box of PAL and the time spent and the distance in the target quadrant in MWM test (P < 0.001 and P < 0.01). Treatment with 7NI attenuated all adverse effects of PTU (P < 0.05 to P < 0.001). PTU lowered BDNF and thiol content and superoxide dismutase (SOD) and catalase (CAT) activities in the brain but increased malondialdehyde (MDA) and nitric oxide (NO) metabolites. In addition, 7NI improved thiol, SOD, CAT, thiol, and BDNF but attenuated MDA and NO metabolites. The results of the current study showed that 7NI improvement in the learning and memory of the hypothyroid juvenile rats, which was accompanied with improving of BDNF and attenuation of NO and brain tissues oxidative damage.

Neuroprotective Effect of Ashwagandha Extract against the Neurochemical Changes Induced in Rat Model of Hypothyroidism

The current aim is to evaluate the effect of ashwagandha root extract (AE) on the neurochemical changes induced in the cortex and hippocampus as a consequence of thyroid dysfunction induced by propylthiouracil (PTU). Male Wistar rats were divided into; control, AE treated rats, rat model of hypothyroidism and rat model of hypothyroidism treated with either AE or L-thyroxine (T4) for 1 month. Rat model of hypothyroidism showed a significant decrease in serum levels of tri-iodothyronine (T3) and T4 and a significant increase in cortical and hippocampal lipid peroxidation (MDA), nitric oxide (NO), superoxide dismutase (SOD) and catalase (CAT). However, reduced glutathione (GSH) decreased significantly. This was associated with a significant increase in hippocampal tumor necrosis factor-α (TNF-α) and cortical dopamine levels. Both L-thyroxine and AE restored T3 and T4 levels. In the hippocampus L-Thyroxine prevented the increase in MDA and restored GSH but failed to restore the increased NO and TNF-α. In the cortex L-thyroxine didn't change the increased MDA and NO and the decreased GSH induced by PTU. L-thyroxine increased cortical and hippocampal SOD and CAT. AE prevented the increased hippocampal MDA, NO and TNF-α and the decreased GSH level induced by PTU. In the cortex AE failed to restore MDA and NO but prevented the decrease in GSH. The increase in cortical dopamine level induced by PTU was ameliorated by L-thyroxine and improved by AE. The present data indicate that AE could prevent thyroid dysfunction and reduce its complications on the nervous system including oxidative stress and neuroinflammation.

Neuroprotective and long term potentiation improving effects of vitamin E in juvenile hypothyroid rats

Protective effects of vitamin E (Vit E) on long term potentiation (LTP) impairment, neuronal apoptosis and increase of nitric oxide (NO) metabolites in the hippocampus of juvenile rats were examined. The rats were grouped (n=13) as: (1) control; (2) hypothyroid (Hypo) and (3) Hypo-Vit E. Propylthiouracil (PTU) was given in drinking water (0.05%) during 6 weeks. Vit E (20 mg/ kg) was daily injected (IP). To evaluate synaptic plasticity, LTP from the CA1 area of the hippocampus followed by high frequency stimulation to the ipsilateral Schafer collateral pathway was carried out. The cortical and hippocampal tissues were then removed to measure NO metabolites. The brains of 5 animals in each group were removed for apoptosis study. The hypothyroidism status decreased the slope, 10-90% slope and amplitude of field excitatory post synaptic potential (fEPSP) compared to the control group (P<0.01-P<0.001). Injection of Vit E increased the slope, 10-90% slope and amplitude of the fEPSP in the Hypo-Vit E group in comparison to the Hypo group (P<0.05-P<0.01). TUNEL positive neurons and NO metabolites were higher in the hippocampus of the Hypo rats, as compared to those in the hippocampus of the control ones (P<0.001). Treatment of the Hypo rats by Vit E decreased apoptotic neurons (P<0.01-P<0.001) and NO metabolites (P<0.001) in the hippocampus compared to the Hypo rats. The results of the present study showed that Vit E prevented the LTP impairment and neuronal apoptosis in the hippocampus of juvenile hypothyroid rats.

Effects of PPAR-γ agonist, pioglitazone on brain tissues oxidative damage and learning and memory impairment in juvenile hypothyroid rats

Aim: The effect of peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist pioglitazone on the brain tissues oxidative damage and learning and memory impairment in the juvenile hypothyroid rats was evaluated. Main methods: Rats were classified as: ( 1 ) Control; (2) Propylthiouracil (PTU); (3) PTU-Pio 10 and (4) PTU-Pio 20. PTU was given in drinking water (0.05%) during 6 weeks. Pioglitazone (10 or 20 mg/kg) was daily injected intraperitoneally. Passive avoidance (PA) and Morris water maze (MMW) were conducted. Later, the animals were sacrificed and the brain tissues were removed for biochemical measurements. Key funding: The results indicated that in the MWM escape latency as well as traveled path increased in the PTU group as compared to the control group. Also, the time spent in the target quadrant in the probe test of MWM and step-through latency in the PA test were decreased in the PTU group as compared to the control group. Pioglitazone reversed all the negative behavioral effects of hypothyroidism. Administration of PTU attenuated thiol and superoxide dismutase (SOD), and catalase (CAT) activities in the brain tissues, whereas increased malondialdehyde (MDA) and nitric oxide (NO) metabolites. PPARγ agonist improved thiol, SOD and CAT, while diminished MDA concentration. Significance: Our finding in the present study indicated that PPARγ agonist pioglitazone prevented the brain tissues from oxidative damage and learning and memory impairments in juvenile hypothyroid rats.

Ameliorating effect of postweaning exposure to antioxidant on disruption of hippocampal neurogenesis induced by developmental hypothyroidism in rats

Developmental hypothyroidism as a model of autism spectrum disorders disrupts hippocampal neurogenesis through the adult stage. The present study investigated the ameliorating effect of postweaning exposure to antioxidant on the hypothyroidism-induced disruptive neurogenesis. Mated female Sprague-Dawley rats were treated with 0 or 10 ppm 6-propyl-2-thiouracil (PTU) as an anti-thyroid agent in drinking water from gestational day 6 to postnatal day (PND) 21 on weaning. PTU-exposed male offspring were fed either basal diet, diet containing α-glycosyl isoquercitrin (AGIQ) at 5,000 ppm or α-lipoic acid (ALA) at 1,000 ppm as an antioxidant from PND 21 to PND 77. PTU-exposure decreased DCX⁺ and NeuN⁺ granule cell lineage subpopulations, synaptic plasticity-related FOS⁺ granule cells, and hilar PVALB⁺ and GAD67⁺ GABAergic interneurons, increased hilar SST⁺ and CALB2⁺ interneurons, and upregulated Gria3, Otx2, and antioxidant enzyme genes in the dentate gyrus on PND 77. These results suggest disruption of neurogenesis remained in relation with increase of oxidative stress and compensatory responses to the disruption at the adult stage. AGIQ recovered expression of some antioxidant enzyme genes and was effective for restoration of NeuN⁺ postmitotic granule cells and PVALB⁺ and SST⁺ interneurons. In contrast, ALA was effective for restoration of all interneuron subpopulations, as well as postmitotic granule cells, and upregulated Grin2a that may play a role for the restoration. Both antioxidants recovered expression of Otx2 and AGIQ-alone recovered Gria3, suggesting a reversal of disruptive neurogenesis by compensatory responses. Thus, postweaning antioxidant exposure may be effective for ameliorating developmental hypothyroidism-induced disruptive neurogenesis by restoring the function of regulatory system.

Experimentally-induced maternal hypothyroidism alters enzyme activities and the sensorimotor cortex of the offspring rats

In this study, we used an experimental model of congenital hypothyroidism to show that deficient thyroid hormones (TH) disrupt different neurochemical, morphological and functional aspects in the cerebral cortex of 15-day-old offspring. Our results showing decreased glutamine synthetase (GS) activity and Ca²⁺ overload in the cerebral cortex of hypothyroid pups suggest misregulated glutamate metabolism associated with developmentally induced TH deficiency. The ¹⁴C-MeAIB accumulation indicates upregulated System A activity and glutamine uptake by neurons. Energy metabolism in hypothyroid cortical slices was preserved, as demonstrated by unaltered glucose metabolism. We also found upregulated acetylcholinesterase activity, depleting acetylcholine from the synaptic cleft, pointing to disrupted cholinergic system. Increased reactive oxygen species (ROS) generation, lipid peroxidation, glutathione (GSH) depletion, which were associated with glutathione peroxidase, superoxide dismutase and gamma-glutamyltransferase downregulation suggest redox imbalance. Disrupted astrocyte cytoskeleton was evidenced by downregulated and hyperphosphorylated glial fibrillary acidic protein (GFAP). Morphological and structural characterization of the sensorimotor cerebral cortex (SCC) showed unaltered thickness of the SCC. However, decreased size of neurons on the layers II & III and IV in the right SCC and increased NeuN positive neurons in specific SCC layers, suggest that they are differently affected by the low TH levels during neurodevelopment. Hypothyroid pups presented increased number of foot-faults in the gridwalk test indicating affected motor functions. Taken together, our results show that congenital hypothyroidism disrupts glutamatergic and cholinergic neurotransmission, Ca²⁺ equilibrium, redox balance, cytoskeleton integrity, morphological and functional aspects in the cerebral cortex of young rats.

Vitamin C prevents hypothyroidism associated neuronal damage in the hippocampus of neonatal and juvenile rats: A stereological study

Hypothyroidism causes an imbalance in antioxidant and pro-oxidants criteria in the brain and enhances the concentration of reactive oxygen species (ROS), and neuronal damage has been observed following an excessive ROS. The main purpose of this study was to examine the preventive effect of vitamin C on hypothyroidism associated neuronal damage in the hippocampus of neonatal and juvenile rats. Pregnant rats after delivery of their pups were randomly divided into four groups and treated with (1) normal drinking water as a control group, (2) Propylthiouracil (PTU) 0.005% added to drinking water, (3-, 4) PTU + Vit C 10 mg/ kg and PTU + Vit C 100 mg/ kg to drinking water. Treatment was carried out during rat's lactation period until to the postnatal day (PND) 60. To assess the histological and stereological changes that occur in this study, brains of 5 male pups were extracted. The number of dark neurons and apoptotic cells in the hippocampal sub-regions of PTU group was significantly greater than the control group's hippocampal sub-regions. In addition, hypothyroidism induced a reduction in the hippocampal volume and increased the numerical density and the total amount of dark neurons. The vitamin C only dose of 100 mg/kg significantly reduced the number of dark neurons and apoptotic cells (P < 0.01) and considerably weakened the influence of hypothyroidism on the volume reduction of the hippocampus (P < 0.05). The current study suggested that vitamin C administration has a possibility to prevent hippocampal neuronal damage caused by neonatal and juvenile hypothyroidism in rats.

The effects of vitamin E on brain derived neurotrophic factor, tissues oxidative damage and learning and memory of juvenile hypothyroid rats

The effects of vitamin E (Vit E) on brain derived neurotrophic factor (BDNF) and brain tissues oxidative damage as well as on learning and memory impairments in juvenile hypothyroid rats were examined. The rats were grouped as: (1) Control; (2) Propylthiouracil (PTU); (3) PTU-Vit E and (4) Vit E. PTU was added to their drinking water (0.05%) during 6 weeks. Vit E (20 mg/kg) was daily injected (IP). Morris water maze (MWM) and passive avoidance (PA) were carried out. The animals were deeply anesthetized and the brain tissues were removed for biochemical measurements. PTU increased the escape latency and traveled path in MWM (P < 0.001). It also shortened the latency to enter the dark compartment of PA as well as the time spent in the target quadrant in probe trial of MWM (P < 0.01-P < 0.001). All the effects of PTU were reversed by Vit E (P < 0.01-P < 0.001). PTU administration attenuated thiol and BDNF content as well as the activities of superoxide dismutase (SOD) and catalase (CAT) in the brain tissues while increased molondialdehyde (MDA). Moreover, Vit E improved BDNF, thiol, SOD and CAT while diminished MDA. The results of the present study showed that Vit E improved BDNF and prevented from brain tissues oxidative damage as well as learning and memory impairments in juvenile hypothyroid rats.

Thymoquinone reverses learning and memory impairments and brain tissue oxidative damage in hypothyroid juvenile rats

In this study, the effect of thymoquinone (TQ) on propylthiouracil (PTU)-induced memory impairment was investigated in juvenile rats. The rats were grouped into control, Hypo, Hypo-TQ5 and Hypo-TQ10. Propylthiouracil increased latency time in the Morris water maze test and decreased delay in entering the dark compartment in the passive avoidance test. Both 5 mg/kg and 10 mg/kg doses of TQ decreased latency time in the Morris water maze test and increased delay in entering the dark compartment in a passive avoidance test. The PTU also increased malondialdehyde and nitric oxide metabolites in the brain while reduced the thiol content and superoxide dismutase and catalase activities and serum T4 level. Both doses of TQ decreased malondialdehyde and nitric oxide metabolites in the brain while enhanced the thiol content and superoxide dismutase and catalase activities and serum T4 level. The results of the present study showed that TQ protected against PTU-induced memory impairments in rats.

α-lipoic acid inhibits oxidative stress in testis and attenuates testicular toxicity in rats exposed to carbimazole during embryonic period

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The intrauterine exposure of carbiamzole (CBZ) on male fertility is not well defined.

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CBZ exposure in utero results in spermatotoxic effects and impaired steroidogenesis in offspring rats at their adulthood.

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Gestational exposure to CBZ augmented testicular oxidative damage in offspring rats.

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α-lipoic acid supplementation with its antioxidant properties ameliorated diminished male reproductive health in rats exposed to CBZ prenatally.

The aim of this study was to evaluate the probable protective effect of α-lipoic acid against testicular toxicity in rats exposed to carbimazole during the embryonic period. Time-mated pregnant rats were exposed to carbimazole from the embryonic days 9–21. After completion of the gestation period, all the rats were allowed to deliver pups and weaned. At postnatal day 100, F1 male pups were assessed for the selected reproductive endpoints. Gestational exposure to carbimazole decreased the reproductive organ indices, testicular daily sperm count, epididymal sperm variables viz., sperm count, viable sperm, motile sperm and HOS-tail coiled sperms. Significant decrease in the activity levels of 3β- and 17β-hydroxysteroid dehydrogenases and expression of StAR mRNA levels with a significant increase in the total cholesterol levels were observed in the testis of experimental rats over the controls. These events were also accompanied by a significant reduction in the serum testosterone levels in CBZ exposed rats, indicating reduced steroidogenesis. In addition, the deterioration of the testicular architecture and reduced fertility ability were noticed in the carbimazole exposed rats. Significant reduction in the activity levels of superoxide dismutase, catalase, glutathione reductase, glutathione peroxidase and reduced glutathione content with a significant increase in the levels of lipid peroxidation were observed in the testis of carbimazole exposed rats over the controls. Conversely, supplementation of α-lipoic acid (70 mg/Kg bodyweight) ameliorated the male reproductive health in rats exposed to carbimazole during the embryonic period as evidenced by enhanced reproductive organ weights, selected sperm variables, testicular steroidogenesis, and testicular enzymatic and non-enzymatic antioxidants. To conclude, diminished testicular antioxidant balance associated with reduced spermatogenesis and steroidogenesis might be responsible for the suppressed reproduction in rats exposed to the carbimazole transplacentally. On the other hand, α-lipoic acid through its antioxidant and steroidogenic properties mitigated testicular toxicity which eventually restored the male reproductive health of carbimazole-exposed rats.

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.

Protective Effect of PPARγ Agonists on Cerebellar Tissues Oxidative Damage in Hypothyroid Rats

The aim of the current study was to investigate the effects of peroxisome proliferator-activated receptor gamma (PPARγ) agonists on cerebellar tissues oxidative damage in hypothyroid rats. The animals included seven groups: group I (control), the animals received drinking water; group II, the animals received 0.05% propylthiouracil (PTU) in drinking water; besides PTU, the animals in groups III, IV, V, VI, and VII, were injected with 20 mg/kg vitamin E (Vit E), 10 or 20 mg/kg pioglitazone, and 2 or 4 mg/kg rosiglitazone, respectively. The animals were deeply anesthetized and the cerebellar tissues were removed for biochemical measurements. PTU administration reduced thiol content, superoxide dismutase (SOD), and catalase (CAT) activities in the cerebellar tissues while increasing malondialdehyde (MDA) and nitric oxide (NO) metabolites. Vit E, pioglitazone, and rosiglitazone increased thiol, SOD, and CAT in the cerebellar tissues while reducing MDA and NO metabolites. The results of present study showed that, similar to Vit E, both rosiglitazone and pioglitazone as PPARγ agonists exerted protective effects against cerebellar tissues oxidative damage in hypothyroid rats.

Do glutathione levels decline in aging human brain?

For the past 60 years a major theory of "aging" is that age-related damage is largely caused by excessive uncompensated oxidative stress. The ubiquitous tripeptide glutathione is a major antioxidant defense mechanism against reactive free radicals and has also served as a marker of changes in oxidative stress. Some (albeit conflicting) animal data suggest a loss of glutathione in brain senescence, which might compromise the ability of the aging brain to meet the demands of oxidative stress. Our objective was to establish whether advancing age is associated with glutathione deficiency in human brain. We measured reduced glutathione (GSH) levels in multiple regions of autopsied brain of normal subjects (n=74) aged one day to 99 years. Brain GSH levels during the infancy/teenage years were generally similar to those in the oldest examined adult group (76-99 years). During adulthood (23-99 years) GSH levels remained either stable (occipital cortex) or increased (caudate nucleus, frontal and cerebellar cortices). To the extent that GSH levels represent glutathione antioxidant capacity, our postmortem data suggest that human brain aging is not associated with declining glutathione status. We suggest that aged healthy human brains can maintain antioxidant capacity related to glutathione and that an age-related increase in GSH levels in some brain regions might possibly be a compensatory response to increased oxidative stress. Since our findings, although suggestive, suffer from the generic limitations of all postmortem brain studies, we also suggest the need for "replication" investigations employing the new (1)H MRS imaging procedures in living human brain.

Thyroid hormone modulates neuroglobin and cytoglobin in rat brain

Thyroid hormones (THs) are essential and crucial for brain development, playing a role in growth and differentiation. Two globins named neuroglobin (Ngb) and cytoglobin (Cygb) are located in the brain, and each one has different distribution and function: They seem to have similar action by providing O(2) for respiratory chain, and detoxification of reactive oxygen species (ROS) and nitric oxide (NO) protecting tissues against irreversible lesions. We aimed to investigate the influence of thyroid state in Ngb and Cygb metabolism in different brain regions and evaluate their responses in cerebellum, hippocampus and cerebral cortex (hereafter called as cortex) after supraphysiological doses at different time points of TH administration. Experiments were carried out in rats, divided in eight experimental groups Control (C), thyroidectomy (Tx), and thyroidectomy treated with jugular intravenous injection (i.v). T3 (100 μl/100 g) injection and sacrificed after 30, 60, 120 min and 6, 12 and 24 h. In cortex, we found increase in Ngb gene and protein expression in different time points compared to C group, however Cygb gene and protein expression were decreased. In hippocampus, Ngb and Cygb protein expression increased 24 h after i.v. T3 injection in comparison to Tx. In cerebellum, we found increased Ngb gene expression after 120 min, 6, 12 and 24 h after T3 administration compared to Tx, and in contrast, protein expression was found to be significantly increased only 12 and 24 h compared to Tx. Ngb and Cygb expression in brain is influenced by thyroid hormone state both by its lack or excess.

Thyroid hormone and astroglia: endocrine control of the neural environment

Thyroid hormones (THs) play key roles in brain development and function. The lack of THs during childhood is associated with the impairment of several neuronal connections, cognitive deficits and mental disorders. Several lines of evidence point to astrocytes as TH targets and as mediators of TH action in the central nervous system; however, the mechanisms underlying these events are still not completely known. In this review, we focus on advances in our understanding of the effects of THs on astroglial cells and the impact of these effects on neurone-astrocyte interactions. First, we discuss the signalling pathways involved in TH metabolism and the molecular mechanisms underlying TH receptor function. Then, we discuss data related to the effects of THs on astroglial cells, as well as studies regarding the generation of mutant TH receptor transgenic mice that have contributed to our understanding of TH function in brain development. We argue that astrocytes are key mediators of hormone actions on development of the cerebral cortex and cerebellum and that the identification of the molecules and pathways involved in these events might be important for determining the molecular-level basis of the neural deficits associated with endocrine diseases.

A mechanistic view of polybrominated diphenyl ether (PBDE) developmental neurotoxicity

Polybrominated diphenyl ethers (PBDEs), extensively used in the past few decades as flame retardants in a variety of consumer products, have become world-wide persistent environmental pollutants. Levels in North America are usually higher than those in Europe and Asia, and body burden is 3-to-9-fold higher in infants and toddlers than in adults. The latter has raised concern for potential developmental toxicity and neurotoxicity of PBDEs. Experimental studies in animals and epidemiological observations in humans suggest that PBDEs may be developmental neurotoxicants. Pre- and/or post-natal exposure to PBDEs may cause long-lasting behavioral abnormalities, particularly in the domains of motor activity and cognition. The mechanisms underlying the developmental neurotoxic effects of PBDEs are not known, though several hypotheses have been put forward. One general mode of action relates to the ability of PBDEs to impair thyroid hormone homeostasis, thus indirectly affecting the developing brain. An alternative or additional mode of action involves a direct effect of PBDEs on nervous system cells; PBDEs can cause oxidative stress-related damage (DNA damage, mitochondrial dysfunction, apoptosis), and interfere with signal transduction (particularly calcium signaling), and with neurotransmitter systems. Important issues such as bioavailability and metabolism of PBDEs, extrapolation of results to low level of exposures, and the potential effects of interactions among PBDE congeners and between PBDEs and other contaminants also need to be taken into account.

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.

Diphenyl diselenide modulates gene expression of antioxidant enzymes in the cerebral cortex, hippocampus and striatum of female hypothyroid rats

INTRODUCTION

Cellular antioxidant signaling can be altered either by thyroid disturbances or by selenium status.

AIMS

To investigate whether or not dietary diphenyl diselenide can modify the expression of genes of antioxidant enzymes and endpoint markers of oxidative stress under hypothyroid conditions.

METHODS

Female rats were rendered hypothyroid by continuous exposure to methimazole (MTZ; 20 mg/100 ml in the drinking water) for 3 months. Concomitantly, MTZ-treated rats were either fed or not with a diet containing diphenyl diselenide (5 ppm). mRNA levels of antioxidant enzymes and antioxidant/oxidant status were determined in the cerebral cortex, hippocampus and striatum.

RESULTS

Hypothyroidism caused a marked upregulation in mRNA expression of catalase, superoxide dismutase (SOD-1, SOD-3), glutathione peroxidase (GPx-1, GPx-4) and thioredoxin reductase (TrxR-1) in brain structures. SOD-2 was increased in the cortex and striatum, while TrxR-2 increased in the cerebral cortex. The increase in mRNA expression of antioxidant enzymes was positively correlated with the Nrf-2 transcription in the cortex and hippocampus. Hypothyroidism caused oxidative stress, namely an increase in lipid peroxidation and reactive oxygen species levels in the hippocampus and striatum, and a decrease in nonprotein thiols in the cerebral cortex. Diphenyl diselenide was effective in reducing brain oxidative stress and normalizing most of the changes observed in gene expression of antioxidant enzymes.

CONCLUSION

The present work corroborates and extends that hypothyroidism disrupts antioxidant enzyme gene expression and causes oxidative stress in the brain. Furthermore, diphenyl diselenide may be considered a promising molecule to counteract these effects in a hypothyroidism state.

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.

Effects of experimentally induced maternal hypothyroidism and hyperthyroidism on the development of rat offspring: II-the developmental pattern of neurons in relation to oxidative stress and antioxidant defense system

Excessive concentrations of free radicals in the developing brain may lead to neurons maldevelopment and neurons damage and death. Thyroid hormones (THs) states play an important role in affecting the modulation of oxidative stress and antioxidant defense system. Thus, the objective of this study was to clarify the effect of hypothyroidism and hyperthyroidism in rat dams on the neurons development of different brain regions of their offspring at several postnatal weeks in relation to changes in the oxidative stress and antioxidant defense system. The adult female rats were administered methimazole (MMI) in drinking water (0.02% w/v) from gestation day 1 to lactation day 21 to induce hypothyroidism and exogenous thyroxine (T4) in drinking water (0.002% w/v) beside intragastric incubation of 50--200 T4 μg/kg body weight (b. wt.) to induce hyperthyroidism. In normal female rats, the sera total thyroxine (TT4) and total triiodothyronine (TT3) levels were detectably increased at day 10 post-partum than those at day 10 of pregnancy. Free thyroxine (FT4), free triiodothyronine (FT3), thyrotropin (TSH) and growth hormone (GH) concentrations in normal offspring were elevated at first, second and third postnatal weeks in an age-dependent manner. In hypothyroid group, a marked depression was observed in sera of dam TT3 and TT4 as well as offspring FT3, FT4 and GH, while there was a significant increase in TSH level with the age progress. The reverse pattern to latter state was recorded in hyperthyroid group. Concomitantly, in control offspring, the rate of neuron development in both cerebellar and cerebral cortex was increased in its density and complexity with age progress. This development may depend, largely, on THs state. Both maternal hypothyroidism and hyperthyroidism caused severe growth retardation in neurons of these regions of their offspring from the first to third weeks. Additionally, in normal offspring, seven antioxidant enzymes, four non-enzymatic antioxidants and one oxidative stress marker (lipid peroxidation, LPO) followed a synchronized course of alterations in cerebrum, cerebellum and medulla oblongata. In both thyroid states, the oxidative damage has been demonstrated by the increased LPO and inhibition of enzymatic and non-enzymatic antioxidants in most examined ages and brain regions. These disturbances in the antioxidant defense system led to deterioration in the neuronal maturation and development. In conclusion, it can be suggested that the maldevelopment of neurons and dendrites in different brain regions of offspring of hypothyroid and hyperthyroid mother rat dams may be attributed, at least in part, to the excess oxidative stress and deteriorated antioxidant defense system in such conditions.

Modulation of antioxidant enzyme expression by PTU-induced hypothyroidism in cerebral cortex of postnatal rat brain

This study aimed to elucidate the effect of 6-n-propylthiouracil (PTU)-induced hypothyroidism on oxidative stress parameters and expression of antioxidant enzymes in cerebral cortex of rat brain during postnatal development. A significant decrease in levels of lipid peroxidation and H(2)O(2) were seen in 7 and 30 days old PTU-treated rats with respect to their controls. Significantly decreased activities of superoxide dismutase (SOD) and catalase (CAT) along with the translated products of SOD1 and SOD2 were observed in 7, 15 and 30 days old PTU-treated rats as compared to their respective controls. However, increase in translated product of CAT was seen in all age groups of PTU-treated rats. Glutathione peroxidase activity was decreased in 7 days and increased in 15 days old PTU-treated rats with respect to their control groups. Histological sections clearly show a decline in neuronal migration with neurons packed together in the hypothyroid group as compared to the control.

Effects of polychlorinated biphenyls on the development of neuronal cells in growth period; structure-activity relationship

Polychlorinated biphenyls (PCBs) are accumulated in our body through food chain and cause a variety of adverse health effects including neurotoxicities such as cognitive deficits and motor dysfunction. In particular, neonates are considered as a high risk group for the neurotoxicity of PCBs exposure. The present study attempted to analyze the structure-activity relationship among PCB congeners and the mechanism of PCBs-induced neurotoxicity. We measured total protein kinase C (PKC) activities, PKC isoforms, reactive oxygen species (ROS), and induction of neurogranin (RC-3) and growth associated protein-43 (GAP-43) mRNA in cerebellar granule cells of neonatal rats with phorbol 12, 13-dibutyrate ([(3)H]PDBu) binding assay, western blot, ROS assay, and reverse transcription PCR (RT-PCR) analysis respectively following the different structural PCBs exposure. Only non-coplanar PCBs showed a significant increase of total PKC-α and βII activity as measured with [(3)H]PDBu binding assay. ROS were more increased with non-coplanar PCBs than coplanar PCBs. The mRNA levels of RC-3 and GAP-43 were more induced with non-coplanar PCBs than coplanar PCBs, indicating that these factors may be useful biomarkers for differentiating non-coplanar PCBs from coplanar PCBs. Non-coplanar PCBs may be more potent neurotoxic congeners than coplanar PCBs. This study provides evidences that non-coplanar PCBs, which have been neglected in the risk assessment processes, should be added in the future to improve the quality and accuracy of risk assessment on the neuroendocrinal adverse effects of PCBs exposures.

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.

PTU-induced hypothyroidism modulates antioxidant defence status in the developing cerebellum

The objective of the present study was to evaluate the effect of 6-n-propylthiouracil (PTU)-induced hypothyroidism on oxidative stress parameters, expression of antioxidant defence enzymes, cell proliferation and apoptosis in the developing cerebellum. PTU challenged neonates showed significant decrease in serum T(3) and T(4) levels and marked increase in TSH levels. Significantly elevated levels of cerebellar H(2)O(2) and lipid peroxidation were observed in 7 days old hypothyroid rats, along with increased activities of superoxide dismutase and glutathione peroxidase and decline in catalase activity. In 30 days old hypothyroid rats, a significant decline in cerebellar lipid peroxidation, superoxide dismutase and glutathione peroxidase activity and expression was observed along with an up-regulation in catalase activity and expression. Expression of antioxidant enzymes was studied by Western blot and semi-quantitative rt-PCR. A distinct increase in cell proliferation as indicated by proliferating cell nuclear antigen (PCNA) immunoreactivity was observed in the internal granular layer of cerebellum of 7 days old hypothyroid rats and significant drop in PCNA positive cells in the cerebellar molecular layer and internal granular layer of 30 days old PTU treated rats as compared to controls. In situ end labeling by TUNEL assay showed increased apoptosis in cerebellum of hypothyroid rats in comparison to controls. These results suggest that the antioxidant defence system of the developing cerebellum is sensitive to thyroid hormone deficiency and consequent alterations in oxidative stress status may play a role in regulation of cell proliferation of the cerebellum during neonatal brain development.

Congenital hypothyroidism is associated with intermediate filament misregulation, glutamate transporters down-regulation and MAPK activation in developing rat brain

Developmental thyroid hormone (TH) deficiency leads to mental retardation and neurological deficits in humans. In this study, congenital hypothyroidism was induced in rats by adding 0.05% 6-propyl-2-thiouracil in the drinking water during gestation and suckling period. This treatment induced hyperphosphorylation of neurofilaments, the neuronal intermediate filament (IF) proteins, of heavy, medium and low molecular weight (NF-H, NF-M and NF-L, respectively) without altering the phosphorylation level of astrocyte IF proteins, glial fibrillary acidic protein (GFAP) and vimentin in cerebral cortex of rats. NF-H was hyperphosphorylated on KSP repeats in the carboxy-terminal tail domain. Furthermore, the immunocontent of GFAP and NF subunits was down-regulated, while vimentin was unaltered both in tissue homogenate and in cytoskeletal fraction of hypothyroid animals. Moreover, we verified the immunocontent of astrocyte glutamate/aspartate transporter (GLAST) and glutamate transporter-1 (GLT-1) as well as activation of mitogen-activated protein kinases (MAPKs) in hypothyroid rats. Results showed that hypothyroidism is associated with decreased GLAST and GLT-1 immunocontent. Additionally, we demonstrated increased extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation without altering Jun N-terminal kinase (JNK) and p38(MAPK) phosphorylation. However, total JNK levels were down-regulated. Taken together, these results suggest that the thyroid status could modulate the integrity of neuronal cytoskeleton acting on the endogenous NF-associated phosphorylating system and that such effect could be related to glutamate-induced excitotoxicity, as well as ERK1/2 and JNK modulation. These events could be somehow related to the neurological dysfunction described in hypothyroidism.

Hypothyroidism induces selective oxidative stress in amygdala and hippocampus of rat

The effects of hypothyroidism on lipid peroxidation (LP), reactive oxygen species (ROS), and nitric oxide synthase (NOS), levels and expression, in rat brain were examined. Hypothyroidism was induced by administering methimazole in drinking water (60 mg/kg/day). In striatum, motor cortex and cerebellum of hypothyroid rats LP was not modified, whereas LP and ROS increased in amygdala and hippocampus of hypothyroid rats at the third week of treatment with methimazole as compared to euthyroid group values. Regarding NOS participation, only hippocampal constitutive-NOS activity was increased, accompanied by an augmentation in nNOS expression. Results show that hypothyroidism induces selective oxidative stress in both the hippocampus and amygdala, where the nitrergic system is involved.

Thyroid hormones states and brain development interactions

The action of thyroid hormones (THs) in the brain is strictly regulated, since these hormones play a crucial role in the development and physiological functioning of the central nervous system (CNS). Disorders of the thyroid gland are among the most common endocrine maladies. Therefore, the objective of this study was to identify in broad terms the interactions between thyroid hormone states or actions and brain development. THs regulate the neuronal cytoarchitecture, neuronal growth and synaptogenesis, and their receptors are widely distributed in the CNS. Any deficiency or increase of them (hypo- or hyperthyroidism) during these periods may result in an irreversible impairment, morphological and cytoarchitecture abnormalities, disorganization, maldevelopment and physical retardation. This includes abnormal neuronal proliferation, migration, decreased dendritic densities and dendritic arborizations. This drastic effect may be responsible for the loss of neurons vital functions and may lead, in turn, to the biochemical dysfunctions. This could explain the physiological and behavioral changes observed in the animals or human during thyroid dysfunction. It can be hypothesized that the sensitive to the thyroid hormones is not only remarked in the neonatal period but also prior to birth, and THs change during the development may lead to the brain damage if not corrected shortly after the birth. Thus, the hypothesis that neurodevelopmental abnormalities might be related to the thyroid hormones is plausible. Taken together, the alterations of neurotransmitters and disturbance in the GABA, adenosine and pro/antioxidant systems in CNS due to the thyroid dysfunction may retard the neurogenesis and CNS growth and the reverse is true. In general, THs disorder during early life may lead to distortions rather than synchronized shifts in the relative development of several central transmitter systems that leads to a multitude of irreversible morphological and biochemical abnormalities (pathophysiology). Thus, further studies need to be done to emphasize this concept.

Differential expression profiles of antioxidant enzymes and glutathione redox status in hyperthyroid rats: a temporal analysis

Our objective was to elucidate a temporal profile of expression of antioxidant enzymes (AOEs) and glutathione redox status in rat liver under the influence of thyroid hormone (T3). The key AOEs, superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx-1) and glutathione reductase (GR) were characterized at transcriptional, translational and biochemical levels after 24 h, 72 h and 120 h of treatment. In general, catalase and GPx-1 showed opposite responses in both transcription and translation. T3 treatment caused tightly coordinated downregulation of catalase. However, transcriptional changes of other AOEs over the different durations of treatment were not always reflected in their respective protein and/or activity levels. Discordance among transcripts, proteins and biological activities of AOEs suggested differential regulation by T3 at multiple levels. Reduced and oxidized glutathione were depleted in hyperthyroid rats. Though T3 exerted a positive stimulatory effect on glucose-6-phosphate dehydrogenase, it was not sufficient to compensate for massive glutathione depletion and impaired activities of GPx-1, GR and GST, disturbing the cellular redox status in the process. Apparently, while transcriptional induction of AOEs might be adaptive responses in conditions of oxidative stress, yet post-transcriptional regulation appeared to be the predominant mechanism of regulation of AOE expression.

Marked recovery of functional metabolic activity and laminar volumes in the rat hippocampus and dentate gyrus following postnatal hypothyroid growth retardation: A quantitative cytochrome oxidase study

Similar to cretinism in human children, absence or deficiency of thyroid hormones in rats and mice during early postnatal development results in marked retardation of brain development along with behavioral and cognitive deficits. Less is known about brain recovery from postnatal hypothyroidism. [Farahvar, A., Meisami, E., 2007. Novel two-dimensional morphometric maps and quantitative analysis reveal marked growth and structural recovery of the rat hippocampal regions from early hypothyroid retardation. Experimental Neurology.] found, by means of morphometric maps, that surface areas of hippocampal cortex and its CA1-CA4 regions which were significantly reduced in developing hypothyroid rats, show nearly complete growth recovery upon restoration of thyroid function. Here we explore the ability of hippocampal synapse-rich neuronal fiber layers to show recovery from early hypothyroid growth retardation. Rat pups were made hypothyroid from birth to day 25 (weaning) or up to young adulthood (day 90) by a treatment with the reversible goitrogen, PTU (n-propylthiouracil), in the drinking water. Recovery was induced by withdrawal of PTU at weaning and analysis of cytochrome oxidase (CytOx)-stained serial sections of the hippocampus and dentate gyrus at the ages of 25 and 90 days. CytOx stains the synapse-rich fiber layers of the hippocampal formation (HCF). Volumetric growth of molecular layer, stratum oriens and radiatum and dentate hilar region showed complete or nearly complete recovery from marked and significant growth retardation induced by early postnatal hypothyroidism. Also the reduced CytOx staining intensity in the hypothyroid rat HCF layers showed marked recovery following hormonal restoration. Results indicate remarkable growth plasticity of the HCF and ability of the synapse-rich fiber layers to show complete recovery of metabolic and functional neural activity from deleterious effects of early hypothyroidism. Mitochondrial CytOx is highly localized to the synapse-rich fiber layers of the HCF and its activity and histochemical staining intensity correlates positively with functional metabolic activity of neural tissue. Thus hippocampus and dentate gyrus neuronal fiber layers and their oxidative activity show remarkable ability to recover from the postnatal hypothyroid growth retardation. The results indicate that some brain regions are less vulnerable to early developmental insults and can recover.

Thyroid hormone promotes glutathione synthesis in astrocytes by up regulation of glutamate cysteine ligase through differential stimulation of its catalytic and modulator subunit mRNAs

To elucidate how thyroid hormone (TH) modulates glutathione (GSH) biogenesis in developing brain, the effect of the hormone on the activity of glutamate cysteine ligase (GCL), previously known as gamma-glutamyl synthetase (gamma-GCS), has been investigated. Hypothyroidism in developing rat brain declined the activity of GCL. Conversely, administration of TH to hypothyroid rats elicited an increase in the activity of the enzyme. TH treatment of astrocytes resulted in a rapid increase in the level of GSH and this up regulation was completely inhibited by L-buthionine S,R-sulfoximine. Kinetics of induction of GCL by TH in astrocytes were closely parallel to that of GSH and the induction was sensitive to both cycloheximide and actinomycin D. Quantitative RT-PCR analysis revealed that astrocytes contained a basal excess of GCLC (catalytic subunit of GCL) mRNA, relative to GCLM (modulator subunit of GCL) mRNA, the ratio being 4:1. TH treatment led to a differential increase in the expression of these two mRNAs, which resulted in a decline in the stoichiometric ratio of GCLC:GCLM mRNA that may favor holoenzyme formation with enhanced catalytic efficiency. TH treatment improved the antioxidative defense in astrocytes by enhancing their hydrogen peroxide scavenging ability with a decrease in peroxide half-life from 7.4 to 4.2 min. The overall results suggest that TH plays a positive role in maintaining GSH homeostasis in astrocytes and in protecting the brain from oxidative stress.

The impact of thyroid activity variations on some oxidizing-stress parameters in rats

The effect of the thyroid activity on the formation of lipid peroxidation and on liver and heart antioxidant enzyme activities was investigated in Wistar rats. Hypothyroidism and hyperthyroidism conditions were induced for five weeks by the administration of 0.05% benzythiouracile (BTU) and L-thyroxine sodium salt (0.0012%), in drinking water, respectively. No significant effect was observed on the rates of both lipid peroxidation and the vitamin E in hepatic and cardiac tissues of hypothyroidism rats compared to the controls, contrary to the hyperthyroidism rats, which expressed a pronounced increase. The increased glutathione peroxidase activity in rats suffering from hyperthyroidism was associated with a fall of the reduced glutathione in the homogenate and a marked increase in the glutathione reductase activity. An increase in superoxide dismutase and catalase activities was also recorded in hyperthyroidism. Our results explain the thyroid activity variation in relation to the lipid peroxidation and the tissular contents of the enzymatic and the non-enzymatic antioxidants. To conclude, our results show the occurrence of a state of oxidizing stress in relation to hyperthyroidism.

Effects of AraC treatment on motor coordination and cerebellar cytoarchitecture in the adult rat

Intact cerebellum cytoarchitecture and cellular communication are indispensable for successful motor coordination and certain forms of memory. Cytosine arabinoside (AraC), often used as an anti-neoplastic agent in humans, can have cerebellum-targeting adverse effects. In order to characterize the nature of AraC-induced cerebellar lesions in an adult rodent model, we have administered AraC (400 mg/kg b.w., i.p.) in adult male Wistar rats for 5 days. The animals' walking pattern, motor coordination, locomotion, spatial navigation and cognition were evaluated, along with neurofilament- and calbindin-like distribution in the cerebellum. AraC-treated rats demonstrated a disturbed walking pattern and a reduced ability of motor learning and coordination, indicative of a mild cerebellar deficit. Although the general locomotion and spatial cognition of AraC-treated rats was not significantly altered, their navigation into the water, in terms of swimming velocity, was irregular, compared to vehicle-treated animals. Neurofilament-like immunostaining was reduced in the molecular cerebellar layer, while calbindin D 28 kDa levels were increased in Purkinje neurons, following AraC treatment. Administration of the antioxidant N-acetylcysteine (NAC) (200 mg/kg b.w., p.o.), for 14 days (prior to and during AraC treatment) largely prevented the AraC-induced behavioral deficits. Our in vivo model of neurotoxicity provides data on the AraC-induced behavioral and cellular alterations concerning the adult rat cerebellum. Furthermore, it provides evidence of a possible neuroprophylactic role of the antioxidant N-acetylcysteine in this model of chemotherapy-induced toxicity.

Negative regulation of superoxide dismutase-1 promoter by thyroid hormone

The role of thyroid hormone [L-3,5,3'-triiodothyronine (T3)] and the thyroid hormone receptor (TR) in regulating growth, development, and metabolic homeostasis is well established. It is also emerging that T3 is associated with oxidative stress through the regulation of the activity of superoxide dismutase-1 (SOD-1), a key enzyme in the metabolism of oxygen free radicals. We found that T3 reverses the activation of the SOD-1 promoter caused by the free radical generators paraquat and phorbol 12-myristate 13-acetate through the direct repression of the SOD-1 promoter by liganded TR. Conversely, the SOD-1 promoter is significantly stimulated by unliganded TRs. This regulation requires the DNA-binding domain of the TR, which is recruited to an inhibitory element between -157 and +17 of the SOD-1 promoter. TR mutations, which abolish recruitment of coactivator proteins, block repression of the SOD-1 promoter. Conversely, a mutation that inhibits corepressor binding to the TR prevents activation. Together, our findings suggest a mechanism of negative regulation in which TR binds to the SOD-1 promoter but coactivator and corepressor binding surfaces have an inverted function. This effect may be important in T3 induction of oxidative stress in thyroid hormone excess.

Thyroid hormone stimulates γ-glutamyl transpeptidase in the developing rat cerebra and in astroglial cultures

Hypothyroidism in the developing rat brain is associated with enhanced oxidative stress, one of the earliest manifestations of which is a decline in the level of glutathione (GSH). To investigate the role of thyroid hormone (TH) on GSH homeostasis, the effect of TH on gamma-glutamyl transpeptidase (gammaGT), the key enzyme involved in the catalysis of GSH, was studied. Hypothyroidism declined the specific activity of cerebral gammaGT at all postnatal ages examined (postnatal day 1-20) with a maximum inhibition of 42% at postnatal day 10. Intraperitoneal injection of TH to 15-day-old rat pups increased the specific activity of gammaGT by 25-30% within 4-6 hr. Treatment of primary cultures of astrocytes by TH also enhanced the specific activity of gammaGT by 30-40% within 4-6 hr. The induction of gammaGT by TH was blocked by actinomycin D or cycloheximide. gammaGT is an ectoenzyme that is normally involved in the catabolism of GSH released by astrocytes. In the presence of the gammaGT-inhibitor, acivicin, GSH released in the culture medium of astrocytes increased linearly for at least 6 hr and TH had no effect on this accumulation pattern. In the absence of acivicin, GSH content of the medium from TH-treated cells was significantly lower than that of untreated controls due to activation of gammaGT by TH and a faster processing of GSH. Because the products of gammaGT reaction are putative precursors for neuronal GSH, the activation of gammaGT by TH may be conducive to GSH synthesis in neurons and their protection from oxidative stress.

The effect of thyroxine administration on lipid peroxidation in different tissues of rats with hypothyroidism

Thyroid dysfunctions bring about pathological changes in different organs of the body. Findings obtained from in vivo and in vitro studies point out that thyroid hormones have a strong impact on oxidative stress. The present study was conducted to demonstrate how high-dose thyroxin administration for one week affected oxidative damage formed in experimental hypothyroidism. The study was carried out with 30 Spraque-Dawley species male rats. The experimental animals were divided into 3 groups (Group 1, control; Group 2, hypothyroidism; Group 3, hypothyroidism + thyroxine administration). Malondialdehyde (MDA) and glutathione (GSH) levels were determined in cerebral, hepatic and cardiac tissues after the experimental period. MDA and GSH levels in cerebral, hepatic and cardiac tissues of hypothyroidism + thyroxine supplemented group were higher than those in the control and hypothyroidism groups (p<0.001). The same parameters were higher in the control group than those in the hypothyroidism group (p<0.001). The results of the present study show that hypothyroidism reduced the oxidative damage in cerebral, hepatic and cardiac tissues of rats. However, high-dose thyroxine administration in addition to induced hypothyroidism increased oxidative damage in the same tissues and that this damage could not be prevented despite the increase in the antioxidant system activity.

Short-term thyroxine administration leads to lipid peroxidation in renal and testicular tissues of rats with hypothyroidism

Thyroid dysfunction brings about pathological changes in different organs of the body. The aim of the present study was to examine how experimental hypothyroidism and additional short-term high-dose thyroxine administration (one-week) affected lipid peroxidation in renal and testicular tissues of rats. The study was carried out on 30 male Spraque-Dawley rats. The experimental animals were divided into 3 groups as control, hypothyroidism and hypothyroidism + thyroxine administration. Both malondialdehyde (MDA) and glutathione (GSH) levels were lower in renal and testicular tissues of the hypothyroidism group than the control and hypothyroidism + thyroxine administration groups and the levels in hypothyroidism + thyroxine administration group were higher than those in the control and hypothyroidism groups (p < 0.001). Results of the study demonstrate that hypothyroidism reduced oxidant stress in kidney and testis tissues, but short-term, high-dose thyroxine administration in addition to hypothyroidism increased oxidant stress in the same tissues of rats.

Antioxidants in patients with hyperthyroidism

Hyperthyroidism is a hypermetabolic state accompanied by increased oxygen utilization, increased production of reactive oxygen species and consequentially measurable changes in antioxidative factors. Therefore, the activities of whole blood glutathione peroxidase (GPx) and erythrocyte superoxide dismutase (SOD), total antioxidant status (TAS) in serum and erythrocytes, and serum urate and transferrrin concentrations were determined in 70 women: 14 with newly diagnosed Graves' disease (group A); 28 with hyperthyroidism on therapy with methimazole (group B, divided into two subgroups, B1 and B2) and 28 healthy women (group C). In comparison with control group C, GPx activity was significantly decreased in all patient groups (p < 0.05), whereas SOD activity was significantly decreased in group A (p < 0.01) and significantly increased in group B (p < 0.01). In comparison with the control group, serum TAS activity was significantly decreased in group A, and erythrocyte TAS activity in all patient groups. Study results suggest that the impaired antioxidative factor balance leads to the development and presence of oxidative stress in women with hyperthyroidism. The severity of these alterations, considered contradictory by some authors, appears to depend on the use of therapy.

Prolonged P300 latency in thyroid failure: a paradox. P300 latency recovers later in mild hypothyroidism than in severe hypothyroidism

This study was performed to analyze quantitatively the cognitive functions of patients with mild and severe hypothyroidism by measuring P300 event-related evoked potentials before and after euthyroidism was established. Patients diagnosed as having Hashimato's thyroiditis with thyroid stimulating hormone (TSH) levels between 5 and 10 mU/L (mild thyroid failure; n = 24) and those with severe hypothyroidism (n = 13) were enrolled randomly to the study protocol. P300-event related potentials were recorded during thyroid insufficiency, and in the first and sixth month of euthyroidism. P300 latencies were prolonged in both the mild and severe hypothyroid patients compared to controls (p = 0.042, p < 0.001, respectively). The overt hypothyroid patients showed significant decrease in their P300 latencies after the first month of euthyroidism (p = 0.001). These P300 latency values did not differ in the subsequent 6-month period. The mild hypothyroid group, however, displayed no improvement of P300 latency in the first month but normalized at the sixth month of euthyroidism. In conclusion, both the overt and the mild hypothyroid patients revealed prolonged P300 latencies. Unexpectedly, P300 latencies in the patients with mild thyroid failure required more time to recover compared to the overt hypothyroid patients. This finding indicates different clinical outcomes of various thyroid insufficiency states on the brain.

Influence of hypothyroidism on lipid peroxidation, erythrocyte resistance and antioxidant plasma properties in rabbits

The effect of hypothyroidism on some oxidative stress parameters is reported. Moderate hypothyroid state was induced in two groups of female rabbits (3 and 12 months old) by giving 50 mg/kg body weight (BW) of propylthiouracil (PTU) per os for 6 days and 20 mg/kg BW of methimazole (MMI) for further 14 days. Serum T4 and T3 concentrations decreased by about 38-40 and 32-36%, respectively. The induced hypothyroidism resulted in a significant decrease in the serum concentration of the lipid peroxidation end-product malondialdehyde, as measured by the thiobarbituric-acid assay. Erythrocytes of hypothyroid animals exhibited higher resistance to oxidative stress, while submitted to free radicals generator 2,2'-azo-bis(2-amidinopropane) hydrochloride (AAPH) in vitro. Using two detector systems (phospholipid liposomes and deoxyribose), sensitive to either organic or inorganic oxygen radical damage, the ability of euthyroid and hypothyroid rabbit plasma to protect against oxygen radicals was evaluated. The plasma of hypothyroid animals showed about 20% higher ability to protect against iron-binding organic radicals, but about 50% lower chain-breaking antioxidant activity. The antioxidant capacity of plasma against inorganic radicals was not affected by hypothyroidism. In conclusion, the results show that thyroid hormones modulate the free-radical-induced oxidative damage of lipids and that hypothyroidism offers some protection against lipid peroxidation.

The nNOS inhibitor, AR-R17477AR, prevents the loss of NF68 immunoreactivity induced by methamphetamine in the mouse striatum

The present study examined the time-course and regionally-selective changes in the levels of the neurofilament protein NF68 in the mouse brain induced by methamphetamine (METH). The ability of low ambient temperature, or of the specific neuronal nitric oxide synthase (nNOS) inhibitor AR-R17477AR, to protect against both long-term striatal NF68 and dopamine loss induced by METH (3 mg/kg, i.p.) was also studied. Seven days after METH administration (3, 6 and 9 mg/kg, i.p., three times at 3 h intervals), mice showed a reduction of about 40% in immunoreactivity for NF68 in the striatum. This effect was not produced in cortex after METH administration at the dose of 3 mg/kg. No difference from controls was observed when measurements were carried out 1 h and 24 h after the last METH injection at the dose of 3 mg/kg. The loss of NF68 immunoreactivity seems to be associated with the long-term dopamine depletion induced by METH, since no change in serotonin concentration is observed in either the striatum or cortex 7 days after dosing. Animals kept at a room temperature of 4 degrees C showed a loss of NF68 similar to those treated at 22 degrees C but an attenuation of dopamine depletion in the striatum. Pre-treatment with AR-R17477AR (5 mg/kg, s.c.) 30 min before each of the three METH (3 mg/kg, i.p.) injections provided complete protection against METH-induced loss of NF68 immunoreactivity and attenuated the decrease in striatal dopamine and HVA concentrations by about 50%. These data indicate that both the reduction of NF68 immunoreactivity and the loss of dopamine concentration are due to an oxidative stress process mediated by reactive nitrogen species, and are not due to changes in body temperature.

Medical differentials with potential behavioral manifestations

Boundaries between behavioral conditions and medical differentials are likely to blur more rather than less as we learn more about genomic, cellular, and subcellular effects on common conditions. These changes should lead to better treatment but may also require a paradigm shift in how we view behavioral conditions and the mechanisms that contribute to them.