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Li AA, Makris SL, Marty MS, Strauss V, Gilbert ME, Blacker A, Zorrilla LM, Coder PS, Hannas B, Lordi S, Schneider S. Practical considerations for developmental thyroid toxicity assessments: What's working, what's not, and how can we do better? Regul Toxicol Pharmacol 2019; 106:111-136. [PMID: 31018155 DOI: 10.1016/j.yrtph.2019.04.010] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2018] [Revised: 04/11/2019] [Accepted: 04/14/2019] [Indexed: 12/26/2022]
Abstract
Thyroid hormones (THs; T3 and T4) play a role in development of cardiovascular, reproductive, immune and nervous systems. Thus, interpretation of TH changes from rodent studies (during pregnancy, in fetuses, neonates, and adults) is critical in hazard characterization and risk assessment. A roundtable session at the 2017 Society of Toxicology (SOT) meeting brought together academic, industry and government scientists to share knowledge and different perspectives on technical and data interpretation issues. Data from a limited group of laboratories were compiled for technical discussions on TH measurements, including good practices for reliable serum TH data. Inter-laboratory historical control data, derived from immunoassays or mass spectrometry methods, revealed: 1) assay sensitivities vary within and across methodologies; 2) TH variability is similar across animal ages; 3) laboratories generally achieve sufficiently sensitive TH quantitation levels, although issues remain for lower levels of serum TH and TSH in fetuses and postnatal day 4 pups; thus, assay sensitivity is critical at these life stages. Best practices require detailed validation of rat serum TH measurements across ages to establish assay sensitivity and precision, and identify potential matrix effects. Finally, issues related to data interpretation for biological understanding and risk assessment were discussed, but their resolution remains elusive.
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Affiliation(s)
- Abby A Li
- Exponent Inc., 1010 14th Street, San Francisco, CA, 94114, USA.
| | - Susan L Makris
- US Environmental Protection Agency Office of Research and Development, 1200 Pennsylvania Ave NW 8623R, Washington, DC, 20460, USA.
| | - M Sue Marty
- The Dow Chemical Company, Toxicology & Environmental Research and Consulting, 1803 Building, Midland, MI, 48674, USA.
| | - Volker Strauss
- BASF SE, Experimental Toxicology and Ecology, 67056, Ludwigshafen, Germany.
| | - Mary E Gilbert
- US Environmental Protection Agency, National Health Environmental Effects Research Lab, 109 T.W. Alexander Drive, MD B105 05, Research Triangle Park, NC, 27711, USA.
| | - Ann Blacker
- Bayer CropScience, P.O. Box 12014, RTP, NC, 27709, USA.
| | | | - Pragati S Coder
- Charles River Laboratories, Developmental and Reproductive Toxicology, 1407 George Road, Ashland, OH, 44805, USA.
| | - Bethany Hannas
- The Dow Chemical Company, Toxicology & Environmental Research and Consulting, 1803 Building, Midland, MI, 48674, USA.
| | - Sheri Lordi
- Charles River Laboratories International, 251 Ballardvale Street, Wilmington, MA, 01887, USA.
| | - Steffen Schneider
- BASF SE, Experimental Toxicology and Ecology, 67056, Ludwigshafen, Germany.
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Murk AJ, Rijntjes E, Blaauboer BJ, Clewell R, Crofton KM, Dingemans MML, Furlow JD, Kavlock R, Köhrle J, Opitz R, Traas T, Visser TJ, Xia M, Gutleb AC. Mechanism-based testing strategy using in vitro approaches for identification of thyroid hormone disrupting chemicals. Toxicol In Vitro 2013; 27:1320-46. [PMID: 23453986 DOI: 10.1016/j.tiv.2013.02.012] [Citation(s) in RCA: 142] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2012] [Revised: 02/07/2013] [Accepted: 02/18/2013] [Indexed: 11/16/2022]
Abstract
The thyroid hormone (TH) system is involved in several important physiological processes, including regulation of energy metabolism, growth and differentiation, development and maintenance of brain function, thermo-regulation, osmo-regulation, and axis of regulation of other endocrine systems, sexual behaviour and fertility and cardiovascular function. Therefore, concern about TH disruption (THD) has resulted in strategies being developed to identify THD chemicals (THDCs). Information on potential of chemicals causing THD is typically derived from animal studies. For the majority of chemicals, however, this information is either limited or unavailable. It is also unlikely that animal experiments will be performed for all THD relevant chemicals in the near future for ethical, financial and practical reasons. In addition, typical animal experiments often do not provide information on the mechanism of action of THDC, making it harder to extrapolate results across species. Relevant effects may not be identified in animal studies when the effects are delayed, life stage specific, not assessed by the experimental paradigm (e.g., behaviour) or only occur when an organism has to adapt to environmental factors by modulating TH levels. Therefore, in vitro and in silico alternatives to identify THDC and quantify their potency are needed. THDC have many potential mechanisms of action, including altered hormone production, transport, metabolism, receptor activation and disruption of several feed-back mechanisms. In vitro assays are available for many of these endpoints, and the application of modern '-omics' technologies, applicable for in vivo studies can help to reveal relevant and possibly new endpoints for inclusion in a targeted THDC in vitro test battery. Within the framework of the ASAT initiative (Assuring Safety without Animal Testing), an international group consisting of experts in the areas of thyroid endocrinology, toxicology of endocrine disruption, neurotoxicology, high-throughput screening, computational biology, and regulatory affairs has reviewed the state of science for (1) known mechanisms for THD plus examples of THDC; (2) in vitro THD tests currently available or under development related to these mechanisms; and (3) in silico methods for estimating the blood levels of THDC. Based on this scientific review, the panel has recommended a battery of test methods to be able to classify chemicals as of less or high concern for further hazard and risk assessment for THD. In addition, research gaps and needs are identified to be able to optimize and validate the targeted THD in vitro test battery for a mechanism-based strategy for a decision to opt out or to proceed with further testing for THD.
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Affiliation(s)
- AlberTinka J Murk
- Wageningen University, Sub-department of Toxicology, Tuinlaan 5, 6703 HE Wageningen, The Netherlands.
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Gianazza E, Vegeto E, Eberini I, Sensi C, Miller I. Neglected markers: Altered serum proteome in murine models of disease. Proteomics 2012; 12:691-707. [DOI: 10.1002/pmic.201100320] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2011] [Accepted: 08/28/2011] [Indexed: 11/09/2022]
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Structure-based investigation on the binding interaction of hydroxylated polybrominated diphenyl ethers with thyroxine transport proteins. Toxicology 2010; 277:20-8. [DOI: 10.1016/j.tox.2010.08.012] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2010] [Revised: 08/16/2010] [Accepted: 08/17/2010] [Indexed: 11/20/2022]
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Hedge JM, DeVito MJ, Crofton KM. In Vivo Acute Exposure to Polychlorinated Biphenyls: Effects on Free and Total Thyroxine in Rats. Int J Toxicol 2009; 28:382-91. [DOI: 10.1177/1091581809344631] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Hypothyroxinemia in rats has been well documented as a result of exposure to polychlorinated biphenyls (PCBs). Hypothetical mechanisms include induction of hepatic catabolic enzymes and cellular hormone transporters, and/or interference with plasma transport proteins. We hypothesized that if thyroxine displacement from transport proteins by PCBs occurs in vivo, it would result in increased free thyroxine (FT4). This study investigates the effects of a single oral dose of 2,2’,4,4’,5,5'-hexachlorobiphenyl (PCB 153 at 60 mg/kg) or 3,3’,4,4’,5,5'-hexachlorobiphenyl (PCB 169 at 1 mg/kg) on rats at 28 or 76 days of age. Total thyroxine (TT4) and FT4 were measured at 0.5, 1, 2, 4, 8, 24, or 48 hours post -dosing. Microsomal ethoxy- and pentoxy-resorufin-O-deethylase (EROD and PROD) activity and uridine diphosphoglucuronosyl transferase (UGT) activity were determined. No significant increase in TT4 or FT4 concentrations was seen at any time point. PCB 153 significantly decreased TT4 and FT4 in young and adult rats, with young rats showing a time-by-treatment interaction from 2 to 48 hours post -dosing in serum FT4. With PCB 169 exposure, young rats showed a decrease in FT4 only, whereas adult rats showed decreases in TT4 only. Hepatic EROD and PROD activities were both dramatically increased following PCB 169 and 153, respectively. Uridine diphosphoglucuronosyl transferase activity was increased only after PCB 169 exposure. These data demonstrate that neither PCB 153 nor PCB169 increased FT4, which supports the conclusion that these PCBs do not displace thyroxine from serum TTR, or if it does occur, there is no subsequent increase in serum FT4 in vivo.
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Affiliation(s)
- J. M. Hedge
- From the Integrated Systems Toxicology Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. E.P.A., Research Triangle Park, NC
| | - M. J. DeVito
- From the Integrated Systems Toxicology Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. E.P.A., Research Triangle Park, NC
| | - K. M. Crofton
- From the Integrated Systems Toxicology Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. E.P.A., Research Triangle Park, NC
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Zoeller RT, Tan SW, Tyl RW. General background on the hypothalamic-pituitary-thyroid (HPT) axis. Crit Rev Toxicol 2007; 37:11-53. [PMID: 17364704 DOI: 10.1080/10408440601123446] [Citation(s) in RCA: 267] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
This article reviews the thyroid system, mainly from a mammalian standpoint. However, the thyroid system is highly conserved among vertebrate species, so the general information on thyroid hormone production and feedback through the hypothalamic-pituitary-thyroid (HPT) axis should be considered for all vertebrates, while species-specific differences are highlighted in the individual articles. This background article begins by outlining the HPT axis with its components and functions. For example, it describes the thyroid gland, its structure and development, how thyroid hormones are synthesized and regulated, the role of iodine in thyroid hormone synthesis, and finally how the thyroid hormones are released from the thyroid gland. It then progresses to detail areas within the thyroid system where disruption could occur or is already known to occur. It describes how thyroid hormone is transported in the serum and into the tissues on a cellular level, and how thyroid hormone is metabolized. There is an in-depth description of the alpha and beta thyroid hormone receptors and their functions, including how they are regulated, and what has been learned from the receptor knockout mouse models. The nongenomic actions of thyroid hormone are also described, such as in glucose uptake, mitochondrial effects, and its role in actin polymerization and vesicular recycling. The article discusses the concept of compensation within the HPT axis and how this fits into the paradigms that exist in thyroid toxicology/endocrinology. There is a section on thyroid hormone and its role in mammalian development: specifically, how it affects brain development when there is disruption to the maternal, the fetal, the newborn (congenital), or the infant thyroid system. Thyroid function during pregnancy is critical to normal development of the fetus, and several spontaneous mutant mouse lines are described that provide research tools to understand the mechanisms of thyroid hormone during mammalian brain development. Overall this article provides a basic understanding of the thyroid system and its components. The complexity of the thyroid system is clearly demonstrated, as are new areas of research on thyroid hormone physiology and thyroid hormone action developing within the field of thyroid endocrinology. This review provides the background necessary to review the current assays and endpoints described in the following articles for rodents, fishes, amphibians, and birds.
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Affiliation(s)
- R Thomas Zoeller
- Biology Department, Morrill Science Center, University of Massachusetts-Amherst, Amherst, Massachusetts 01003, USA.
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Miller I, Haynes P, Gemeiner M, Aebersold R, Manzoni C, Lovati MR, Vignati M, Eberini I, Gianazza E. Proteins of rat serum: II. Influence of some biological parameters of the two-dimensional electrophoresis pattern. Electrophoresis 1998; 19:1493-500. [PMID: 9694301 DOI: 10.1002/elps.1150190846] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
This report complements the database already detailed for serum proteins of healthy adult male rats (P. Haynes et al., Electrophoresis 1998, 19, 1484-1492). The influence on the two-dimensional electrophoresis (2-DE) pattern of certain physiological conditions (sex, age) was studied as well as of changes in thyroid metabolism. We have extended the information about the major components of rat serum by identifying the proteins typical for the response to acute inflammation. Analyzing 27 spots, six proteins not found in control sera could be recognized; migration at overlapping or close positions with five already characterized proteins was observed for some. A compilation of all our rat data can be accessed through: http://weber.u.washington.edu/ruedilab/ aebersold.html.
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Affiliation(s)
- I Miller
- Veterinärmedizinische Universität, Institut für Medizinische Chemie, Wien, Austria
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Morse DC, Van Bladeren PJ, Klasson Wehler E, Brouwer A. beta-Naphthoflavone- and self-induced metabolism of 3,3',4,4'-tetrachlorobiphenyl in hepatic microsomes of the male, pregnant female and foetal rat. Xenobiotica 1995; 25:245-60. [PMID: 7618351 DOI: 10.3109/00498259509061849] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
1. The in vitro metabolism of 3,3',4,4'-tetrachloro-[14C]-biphenyl ([14C]-TCB) by hepatic microsomes from the Wistar rat was investigated with liver microsomes from the male, pregnant female and foetus. 2. Three hydroxylated metabolites (4-OH-3,3',4,5'-tetrachlorobiphenyl, 5-OH-3,3',4,4'-tetrachlorobiphenyl, and 6-OH-3,3',4,4'-tetrachlorobiphenyl) were identified by hplc and gc-ms after incubations of liver microsomes from the beta-naphthoflavone-pretreated male rat and TCB-treated pregnant rat. No metabolites of [14C]-TCB were found after incubation with foetal liver microsomes from dams pretreated with [14C]-TCB. The results indicate that the in vivo accumulation of 4-OH-tetraCB in the foetal compartment is probably due to transplacental transport rather than the formation of this metabolite in the foetus. 3. Pretreatment of the male rat with beta-naphthoflavone substantially induced the formation of hydroxylated metabolites, but pretreatment with phenobarbital and dexamethasone was without effect. Based on in vitro incubations of liver microsomes from the beta-naphthoflavone pretreated male rat, an apparent Km and Vmax of 4.5 microM and 240 pmol/mg protein/min respectively was determined for the metabolism of [14C]-TCB. The formation of phenolic metabolites of [14C]-TCB was most likely dependent on P4501A induction.
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Affiliation(s)
- D C Morse
- Department of Toxicology, Agricultural University, Wageningen, The Netherlands
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Abstract
Thyroxine secretion rates (TSR) at various stages of pregnancy in rats were measured by the radiothyroxine pool-turnover method. Groups of rats included normal controls (non-pregnant), days 5, 10, 20, and 22 of pregnancy and near term (within 24 hours prior to parturition if past 22 days of pregnancy). Each animal had blood samples taken just prior to injection of 10 microCi L-thyroxine (L-T4)-131I and at 12, 24, 36, and 48 hours afterwards. Determinations of thyroxine iodine (T4-I), volume of distribution (VD), fractional turnover rate (K), and L-T4 pool size were made from these samples. TSR was calculated as the product of (1.54) (T4-I) (VD) (K). An increase in TSR occurred near term, 3.65 micrograms L-T4/day compared to 1.23 micrograms L-T4/day in the controls, was primarily due to an increase in VD from 33.9 ml in the controls to 90.0 ml near term. A rapid increase in TSR to 3.65 micrograms L-T4/day just prior to term was postulated to be due to a stimulatory action of relaxin in the presence of estrogen upon L-T4 utilization. The mechanism of the increase in TSR in pregnant rats is probably due to the effect of several hormonal changes in maternal tissues throughout pregnancy and to adaptation of the pregnant animals to higher metabolic needs of the rapid developing fetuses.
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Affiliation(s)
- M H Lu
- Department of Dairy Husbandry University of Missouri-Columbia 65201
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Lans MC, Spiertz C, Brouwer A, Koeman JH. Different competition of thyroxine binding to transthyretin and thyroxine-binding globulin by hydroxy-PCBs, PCDDs and PCDFs. Eur J Pharmacol 1994; 270:129-36. [PMID: 8039542 DOI: 10.1016/0926-6917(94)90054-x] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
In an earlier study several hydroxylated polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) competitively displaced [125I]thyroxine (T4) from transthyretin with different potencies. Transthyretin is the major T4 transport protein in plasma of rodents. In man, however, thyroxine-binding globulin transports most of the T4 in blood. In this study, hydroxylated PCBs, PCDDs and PCDFs were tested in an in vitro competitive binding assay, using purified human thyroxine-binding globulin and [125I]T4 as the displaceable radioligand. None of the tested hydroxylated PCBs, PCDDs and PCDFs inhibited [125I]T4 binding to thyroxine-binding globulin. In addition, some T4 derived compounds, e.g., tyrosine, mono-iodotyrosine, di-iodotyrosine and tri-iodophenol were tested on both transthyretin and thyroxine-binding globulin to investigate possible differences in structural characteristics determining T4 binding to thyroxine-binding globulin and transthyretin. The T4 derived compounds also did not inhibit [125I]T4 binding to thyroxine-binding globulin as tested in the in vitro assay. However, tri-iodophenol and to a lesser extent di-iodotyrosine inhibited [125I]T4-transthyretin binding. These results indicate a marked difference in T4 binding to thyroxine-binding globulin or transthyretin. The hydroxylated PCBs, PCDDs and PCDFs can inhibit T4 binding to transthyretin, but not to thyroxine-binding globulin, and thus may cause different effects in rodents and man.
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Affiliation(s)
- M C Lans
- Department of Toxicology, Agricultural University Wageningen, Netherlands
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Affiliation(s)
- L Bartalena
- Istituto di Endocrinologia, Università di Pisa, Italy
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Pavgi S, Licht P. Measurement of plasma thyroxine binding protein in relation to thyroidal condition in the turtle, Trachemys scripta, by radioimmunoassay. Gen Comp Endocrinol 1992; 85:147-55. [PMID: 1563614 DOI: 10.1016/0016-6480(92)90182-j] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Polyclonal (rabbit) antisera were generated against a high-affinity plasma thyroxine (T4) binding protein (TBP) purified from the turtle, Trachemys scripta, and used to develop a specific radioimmunoassay (RIA). The RIA demonstrated the presence of an immunochemically related protein in the plasma of several other species of Trachemys and in members of several other genera from the same family, Emydidae. Plasma from all nonemydids and some emydid genera either showed no competition or nonparallelism in RIA. The presence and level of radioimmunoassayable TBP in diverse species correlated with results of previous comparative measurements of T4 binding activity. However, an immunoreactive protein of the same molecular weight as TBP was identified in all turtles by Western blot analysis. More detailed studies in T. scripta demonstrated that variations in plasma T4 binding activity induced by experimental or environmental manipulations were related to differences in TBP concentrations. The concentration of TBP varied by orders of magnitude (from less than 1 to ca. 150 mg/liter) in euthyroid animals; levels showed ontogenetic changes (virtually absent in hatchlings) and were directly related to thyroidal status. Experimentally induced hypothyroidism (goitrogen treatment or surgical thyroidectomy) resulted in a marked suppression of TBP, and T4 treatment prevented its decline or reinstated it. Thus, in the turtle, this T4 transport protein may exist in higher concentrations and its levels are more variable and show a different relationship to thyroid activity than the analogous T4 binding globulin (TBG) in mammals.
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Affiliation(s)
- S Pavgi
- Department of Integrative Biology, University of California, Berkeley 94720
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Savu L, Vranckx R, Rouaze-Romet M, Maya M, Nunez EA, Tréton J, Flink IL. A senescence up-regulated protein: the rat thyroxine-binding globulin (TBG). BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1097:19-22. [PMID: 1907201 DOI: 10.1016/0925-4439(91)90017-4] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Thyroxine-binding globulin (TBG), the major carrier of thyroid hormones in human serum, was thought to be absent in most species, including rodents. We demonstrated recently that in fact the rat possesses a TBG gene, virtually non-expressed in young adults, but actively transcribed during post-natal development. We now find that the TBG gene is also increasingly re-expressed during senescence. Evidence is presented suggesting that physiologically decreased thyroid hormone levels, characteristic of neonates and of ageing rats, might constitute a common factor inducing up-regulation of TBG in both developmental and ageing processes. Rat TBG is to our knowledge the first biochemical 'positive' (i.e. increasing) marker of non-pathological senescence, expressed at both biosynthetic and bloodstream levels.
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Affiliation(s)
- L Savu
- U.224, INSERM Faculté de Médecine Xavier Bichat, Laboratoire de Biochimie, Paris, France
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Vranckx R, Savu L, Maya M, Nunez EA. Characterization of a major development-regulated serum thyroxine-binding globulin in the euthyroid mouse. Biochem J 1990; 271:373-9. [PMID: 1700701 PMCID: PMC1149564 DOI: 10.1042/bj2710373] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We confirm our finding of a major development-regulated thyroxine-binding globulin (TBG) in the serum of the euthyroid mouse and investigate a number of its binding, structural and regulatory properties. Between 16 days foetal and 60 days postnatal life, the thyroxine (T4)- and tri-iodothyronine (T3)-binding activities of the sera show a striking ontogenic pattern: the binding is 2-3 times higher in foetuses than in mothers, then further increases after birth, reaching between 3 and 5 days maximum values which are 7-8 times higher than the adult ones. This pattern is not correlated with the ontogenesis of the acknowledged specific (transthyretin, TTR) and non-specific (albumin, alpha 1-foetoprotein) thyroid-hormone carriers of the mouse sera. PAGE studies demonstrate that the protein responsible for the elevated binding of the perinatal period is an alpha 1-globulin, with a migration similar to that of human and rat TBGs. Scatchard analysis is consistent with the notions that the T4-binding sites of TBG have high association constants, about two orders of magnitude above the T4 sites of TTR (10(9) M-1 as against 10(7) M-1) and low capacities (37 and 4 nmol/g of serum proteins in pups and adults respectively). Isoelectric focusing (i.e.f.) demonstrates that mouse TBG is a microheterogeneous protein separable, as a function of the pH gradient, in up to 10-12 isoforms, Marked shifts of the relative abundance of isoforms in the course of development are evidenced. The modulation of the TBG binding activity by non-esterified fatty acids (NEFA) and the control of its synthesis by the thyroid status are also reported. Mono- and poly-unsaturated NEFAs are strong inhibitors of the TBG, although they affect TTR less readily. On the other hand, the biosynthesis and/or secretion of TBG, but not of TTR, is under thyroid-hormone control, experimental hypothyroidism inducing a marked increase of the serum TBG. The TBG of mouse behaves as a highly significant parameter of development, pointing to a likely important function of the protein in the process of maturation. Our finding of major TBGs in both euthyroid rats and mice suggests that TBG is more widely spread than was thought until now, but difficult to detect in certain species outside definite maturation stages.
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Affiliation(s)
- R Vranckx
- U.224, INSERM, CNRS, Faculté de Médecine Xavier Bichat, Laboratoire de Biochimie, Paris, France
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Vranckx R, Rouaze M, Savu L, Nunez EA, Beaumont C, Flink IL. The hepatic biosynthesis of rat thyroxine binding globulin (TBG): demonstration, ontogenesis, and up-regulation in experimental hypothyroidism. Biochem Biophys Res Commun 1990; 167:317-22. [PMID: 2106883 DOI: 10.1016/0006-291x(90)91767-m] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Using a human thyroxine binding globulin (TBG) cDNA probe, we demonstrate that rat liver contains two TBG mRNA species of different length, consisting of about 1.8 Kb and 2.4 Kb respectively. Slot blot analysis of the hepatic mRNAs from rats of different age reveals a fair correlation between the developmental trend of the messengers and that of the TBG circulating levels. Finally Northern blot and slot studies demonstrate that the increase of serum TBG induced in adults by thyroidectomy actually reflects an enhanced hepatic biosynthesis of the protein.
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Affiliation(s)
- R Vranckx
- Unité INSERM 224, Faculté de Médecine Xavier Bichat, Paris, France
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