Cadmium induced thyroid dysfunction in chicken: hepatic type I iodothyronine 5'-monodeiodinase activity and role of lipid peroxidation

Cadmium exposure and thyroid hormone disruption: a systematic review and meta-analysis

INTRODUCTION

This meta-analysis aimed to analyze the effect of cadmium (Cd) exposure on thyroid hormone disruption.

CONTENT

Databases including PubMed, Embase, Cochrane Library, and Scopus were searched for studies published up to December 14, 2022. Studies evaluating the association between Cd exposure (blood Cd [BCd] or urine Cd [UCd]) and thyroid function (thyroid-stimulating hormone [TSH], free thyroxine [FT4], total triiodothyronine [TT3]) or thyroid autoimmunity (thyroglobulin antibody [TgAb] or thyroperoxidase Ab [TPOAb]) were included.

SUMMARY AND OUTLOOK

This systematic review included 12 cross-sectional studies. Cd exposure showed a neutral association with TSH (pooled correlation=0.016, 95 % confidence interval [CI]=-0.013 to 0.045, p=0.277), FT4 (pooled correlation=0.028, 95 % CI=-0.005 to 0.061, p=0.098), and thyroid autoimmunity (pooled odds ratio=1.143, 95 % CI=0.820-1.591, p=0.430). However, Cd exposure showed a positive association with TT3 (pooled correlation=0.065, 95 % CI=0.050-0.080, p<0.001), which was consistent with the BCd and UCd subgroup analyses (pooled correlation=0.053 and 0.081, respectively, both p<0.001). Cd exposure was not associated with TSH, FT4, or thyroid autoimmunity but tended to increase with TT3.

Dose-Dependent Cytotoxicity of Polypropylene Microplastics (PP-MPs) in Two Freshwater Fishes

The massive accumulation of plastics over the decades in the aquatic environment has led to the dispersion of plastic components in aquatic ecosystems, invading the food webs. Plastics fragmented into microplastics can be bioaccumulated by fishes via different exposure routes, causing several adverse effects. In the present study, the dose-dependent cytotoxicity of 8−10 μm polypropylene microplastics (PP-MPs), at concentrations of 1 mg/g (low dose) and 10 mg/g dry food (high dose), was evaluated in the liver and gill tissues of two fish species, the zebrafish (Danio rerio) and the freshwater perch (Perca fluviatilis). According to our results, the inclusion of PP-MPs in the feed of D. rerio and P. fluviatilis hampered the cellular function of the gills and hepatic cells by lipid peroxidation, DNA damage, protein ubiquitination, apoptosis, autophagy, and changes in metabolite concentration, providing evidence that the toxicity of PP-MPs is dose dependent. With regard to the individual assays tested in the present study, the biggest impact was observed in DNA damage, which exhibited a maximum increase of 18.34-fold in the liver of D. rerio. The sensitivity of the two fish species studied differed, while no clear tissue specificity in both fish species was observed. The metabolome of both tissues was altered in both treatments, while tryptophan and nicotinic acid exhibited the greatest decrease among all metabolites in all treatments in comparison to the control. The battery of biomarkers used in the present study as well as metabolomic changes could be suggested as early-warning signals for the assessment of the aquatic environment quality against MPs. In addition, our results contribute to the elucidation of the mechanism induced by nanomaterials on tissues of aquatic organisms, since comprehending the magnitude of their impact on aquatic ecosystems is of great importance.

Role of Oxidative Stress and the Identification of Biomarkers Associated With Thyroid Dysfunction in Schizophrenics

Background: Schizophrenia is associated with a deficiency of dietary antioxidants like vitamin B6, B9, and B12 resulting in defective methylation leading to hyperhomocysteinemia. Hyperhomocysteinemia causes mitochondrial DNA damage, oxidative stress, vascular damage, and lipid peroxidation. Oxidative stress and increase in reactive oxygen species result in 8-oxodG production which induces apoptosis of both astrocytes and thyrocytes thus predisposing them to thyroid dysfunction and neurodegeneration. Furthermore, the presence of excessive free radicals increases thyroid thermogenesis causing hyperthyroidism or its excess may cause hypothyroidism by inhibiting iodide uptake. In the present study, we evaluated the various biomarkers associated with thyroid dysfunction in schizophrenics. Materials and Methods: 288 patients suffering from schizophrenia and 100 control subjects were screened for liver function tests (LFTs) such as alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), and total bilirubin (TB). Also, the stress markers, namely malondialdehyde (MDA), homocysteine, cysteine, methionine, the thyroid profile including triiodothyronine (T3), thyroxine (T4), thyroid-stimulating hormone (TSH), thyroxine peroxide antibody (TPO-Ab); TSH receptor-Ab (TSHr-Ab), dietary antioxidants, lipids, cytokines, aminoacids and hormones, vitamins and trace elements, and other biochemical parameters. Results: The LFTs showed elevated levels of ALT (45.57 ± 4.87 Vs. 26.41 ± 3.76 U/L), AST (40.55 ± 1.34 Vs. 21.92 ± 3.65 U/L), ALP (121.54 ± 4.87 Vs. 83.76 ± 5.87 U/L), and total bilirubin (2.63 ± 0.987 Vs. 1.10 ± 0.056 mg/dl), in schizophrenics than controls. Increased levels of MDA (3.71 ± 0.967 Vs. 1.68 ± 0.099) and homocysteine (17.56 ± 2.612 Vs. 6.96 ± 1.987 μmol/L were observed in schizophrenics compared to the controls, indicating increased stress. Levels of cysteine and methionine were decreased in schizophrenics than the controls (1.08 ± 0.089 Vs. 4.87 ± .924 μmol/L and 17.87 ± 1.23 Vs. 99.20 ± 5.36 μmol/L). The levels of TPO-Ab (IU/ml), Tg-Ab (pmol/L), and TSHr-Ab (IU/L) were observed to be higher in the patients' group as compared to control subjects (9.84 ± 2.56 Vs. 5.81 ± 1.98, 55.50 ± 2.98 Vs. 32.95 ± 2.87 and 2.95 ± 0.0045 Vs. 1.44 ± 0.0023 respectively). Levels of Vitamin B6, B9, and B12 were also significantly decreased in the patients compared to the healthy controls. Conclusion: The schizophrenics, demonstrated altered liver function, increased stress markers, and decreased dietary antioxidants. Reduced primary and secondary antioxidant levels, may result in hyperhomocysteinemia and cause further DNA and mitochondrial damage. Therefore, homocysteine and/or prolactin levels may serve as candidate prognostic markers for schizophrenia. Also, both neurological symptoms and the susceptibility to thyroid disorders may be prevented in the initial stages of this debilitating disorder by appropriate dietary supplementation of antioxidants which can rectify a reduction in primary and secondary antioxidants, and disturbed prolactin-serotonin-dopamine interactions in schizophrenics.

A review of metal-induced effects on vitamins A, E and D3 in birds

Birds have been historically affected by metals and are considered powerful sentinels of environmental pollution. Some toxic elements (Pb, Cd, Hg, As) have been broadly studied in avian species and are well known for their accumulation capacity and deleterious effects, including alterations in vitamin levels. Vitamins A, E and D3 are fat-soluble nutrients involved in multiple physiological functions (e.g., immune function, vision, reproduction, growth and development). Publications reporting metal-induced effects on vitamins in birds are growing and, in some cases, results seem contradictory, making them difficult to interpret. Therefore, a clear view of the overall picture is needed. This mini-review article aims to compile relevant data and describe current knowledge on the effects of the most toxic elements (i.e., Pb, Cd, Hg, As) on vitamins A, E and D3 in birds. Although vitamins are diet dependent, they are strongly regulated and transformed in the organism, and metal-related disruption in their homeostasis may provoke alterations in different directions. Moreover, vitamin status and form in vivo is the result of complex interacting processes in the organism and metal exposure may produce cascade effects. Different factors that may contribute to the variable response of vitamins to metals in birds are discussed. Some final remarks and recommendations are provided for future studies. This mini-review shows an overview of the current knowledge in metal-induced alterations in vitamins of special concern for avian ecotoxicology, a research discipline facing important challenges in the coming years.

Transgenerational endocrine disruption: Does elemental pollution affect egg or nestling thyroid hormone levels in a wild songbird?

Endocrine disrupting chemicals (EDCs) include a wide array of pollutants, such as some metals and other toxic elements, which may cause changes in hormonal homeostasis. In addition to affecting physiology of individuals directly, EDCs may alter the transfer of maternal hormones to offspring, i.e. causing transgenerational endocrine disruption. However, such effects have been rarely studied, especially in wild populations. We studied the associations between environmental elemental pollution (As, Cd, Cu, Ni, Pb) and maternally-derived egg thyroid hormones (THs) as well as nestling THs in great tits (Parus major) using extensive sampling of four pairs of polluted and reference populations across Europe (Finland, Belgium, Hungary, Portugal). Previous studies in these populations showed that breeding success, nestling growth and adult and nestling physiology were altered in polluted zones compared to reference zones. We sampled non-incubated eggs to measure maternally-derived egg THs, measured nestling plasma THs and used nestling faeces for assessing local elemental exposure. We also studied whether the effect of elemental pollution on endocrine traits is dependent on calcium (Ca) availability (faecal Ca as a proxy) as low Ca increases toxicity of some elements. Birds in the polluted zones were exposed to markedly higher levels of toxic elements than in reference zones at the populations in Finland, Belgium and Hungary. In contrast to our predictions, we did not find any associations between overall elemental pollution, or individual element concentrations and egg TH and nestling plasma TH levels. However, we found some indication that the effect of metals (Cd and Cu) on egg THs is dependent on Ca availability. In summary, our results suggest that elemental pollution at the studied populations is unlikely to cause overall TH disruption and affect breeding via altered egg or nestling TH levels with the current elemental pollution loads. Associations with Ca availability should be further studied.

T-screen and yeast assay for the detection of the thyroid-disrupting activities of cadmium, mercury, and zinc

In the present study, a two-hybrid yeast bioassay and a T-screen were used to screen for the thyroid receptor (TR)-disrupting activity of select metallic compounds (CdCl2, ZnCl2, HgCl2, CuSO4, MnSO4, and MgSO4). The results reveal that none of the tested metallic compounds showed TR-agonistic activity, whereas ZnCl2, HgCl2, and CdCl2 demonstrated TR antagonism. For the yeast assay, the dose-response relationship of these metallic compounds was established, and the concentrations producing 20 % of the maximum effect of ZnCl2, HgCl2, and CdCl2 were 9.1 × 10(-5), 3.2 × 10(-6), and 1.2 × 10(-6) mol/L, respectively. The T-screen also supported the finding that ZnCl2, HgCl2, and CdCl2 decreased the cell proliferation at concentrations ranging from 10(-6) to 10(-4) mol/L. Furthermore, the thyroid-disrupting activity of metallic compounds in environmental water samples collected from the Guanting Reservoir, Beijing, China was evaluated. Solid-phase extraction was used to separate the organic extracts, and a modified two-hybrid yeast bioassay revealed that the metallic compounds in the water samples could affect thyroid hormone-induced signaling by decreasing the binding of the thyroid hormone. The addition of ethylenediaminetetraacetic acid (30 mg/L) could eliminate the effects. Thus, the cause(s) of the thyroid toxicity in the water samples appeared to be partly related to the metallic compounds.

Relationship between blood cadmium, lead, and serum thyroid measures in US adults - the National Health and Nutrition Examination Survey (NHANES) 2007-2010

Experimental studies have shown that both cadmium (Cd) and lead have potent endocrine disrupting activity. However, studies on whether these heavy metals disrupt thyroid system in humans, especially in general populations with low levels of exposure, are sparse. The study analyzed 6,231 participants aged 20 and older with measurements from 2007-2010 of the National Health and Nutrition Examination Survey (NHANES) to investigate whether whole blood Cd and lead level are associated with serum thyroid hormones measures. Our study suggests that thyroid function may be disrupted by both Cd and lead exposures in the general population and the specific roles of Cd and lead exposure on thyroid axis may differ by sex. However, the mechanisms by which these heavy metals may disrupt thyroid system function in general population needs to be further investigated.