Cobalt-protoporphyrin suppresses thyroid and testicular hormone concentrations in rat serum: a novel action of this synthetic heme analogue

Treatment of rats with Co-protoporphyrin, a synthetic metalloporphyrin which produces a marked and sustained induction of hepatic heme oxygenase and decline in cellular cytochrome P-450 content, caused a significant reduction in serum testosterone, serum thyroxine (T4) and 3,5,3'-triiodothyronine (T3) levels. These endocrine changes were not accompanied by reciprocal elevations in either serum luteinizing hormone (LH) or thyroid-stimulating hormone (TSH) concentrations. Seminal vesicles from Co-protoporphyrin-treated animals were atrophic. The pituitary response to luteinizing hormone-releasing hormone (LHRH) in Co-protoporphyrin-treated animals was moderately attenuated (approximately equal to 50%) but the response to thyrotropin-releasing hormone (TRH) was normal. These findings suggest that at least part of the effects of the metalloporphyrin are mediated at the level of the hypothalamus, such that suppression of serum levels of testosterone, T4 and T3 fails to elicit compensatory pituitary outputs of the respective trophic hormones. It is not known whether these effects are due to direct actions of Co-protoporphyrin on the endocrine system or whether they are secondary consequences of other metabolic derangements, such as those related to the pronounced cellular depletion of heme and cytochrome P-450 caused by the synthetic metalloporphyrin.     

Hedgehog-mediated regulation of thyroid hormone action through iodothyronine deiodinases

INTRODUCTION: The three iodothyronine deiodinases catalyze the metabolic pathway that removes one iodine residue from the T4 molecule, thus producing either the active T3 or the inactive metabolite rT3. Hence, deiodination is a potent mechanism by which to modulate thyroid hormone (TH) action at cellular level, thereby allowing cells to customize their own T3 availability, both spatially and temporally, irrespective of TH serum concentrations. Sonic hedgehog (Hh) regulates patterning and growth of a remarkable variety of tissues throughout embryogenesis. Its constitutive activation is associated with cancer development. AREAS COVERED: Recent evidences from two independent systems implicate the Hh signaling pathway in regulation of TH action via modulation of deiodinase expression. Interestingly, many critical developmental events, for example, amphibian metamorphosis, are tightly regulated by the TH and Hh signaling pathways. This review provides an overview of recent data referring to the intricate regulation of deiodinase activity and intracellular TH action by the Hh pathway. EXPERT OPINION: This functional cross-talk provides a paradigm for interaction between two key signaling pathways critical during development and neoplastic transformation. This interaction may be relevant in other tissues and situations in which the two signaling pathways participate. Deciphering these mechanisms constitutes an exciting field for future research.     

Hedgehog-mediated regulation of thyroid hormone action through iodothyronine deiodinases

Introduction: The three iodothyronine deiodinases catalyze the metabolic pathway that removes one iodine residue from the T4 molecule, thus producing either the active T3 or the inactive metabolite rT3. Hence, deiodination is a potent mechanism by which to modulate thyroid hormone (TH) action at cellular level, thereby allowing cells to customize their own T3 availability, both spatially and temporally, irrespective of TH serum concentrations. Sonic hedgehog (Hh) regulates patterning and growth of a remarkable variety of tissues throughout embryogenesis. Its constitutive activation is associated with cancer development.

Areas covered: Recent evidences from two independent systems implicate the Hh signaling pathway in regulation of TH action via modulation of deiodinase expression. Interestingly, many critical developmental events, for example, amphibian metamorphosis, are tightly regulated by the TH and Hh signaling pathways. This review provides an overview of recent data referring to the intricate regulation of deiodinase activity and intracellular TH action by the Hh pathway.

Expert opinion: This functional cross-talk provides a paradigm for interaction between two key signaling pathways critical during development and neoplastic transformation. This interaction may be relevant in other tissues and situations in which the two signaling pathways participate. Deciphering these mechanisms constitutes an exciting field for future research.     

甲状腺激素对免疫抑制药物作用的影响

甲状腺片(150mg.kg~(-1).d~(-1),ig×10d和200mg.kg~(-1).d~(-1),ig×10d)能显著促进正常成年小鼠对二硝基氯苯(DNCB)所致的皮肤迟发型超敏反应(DH)。在连续应用甲状腺片200mg.kg~(-1).d~(-1)ip×10d的小鼠,环磷酰胺(25mg.kg~(-1).kg~(-1)ip×10d和30mg.kg~(-1).d~(-1),ip×10d)以及氢化可的松(25mg.kg~(-1).d~(-1),im×10d)抑制小鼠的DNCB所致DH的作用减弱甚至消失。     

Non-clinical pharmacokinetic profiles of rovatirelin,an orally available thyrotropin-releasing hormone analogue

1. The non-clinical pharmacokinetic profiles of rovatirelin, a novel thyrotropin-releasing hormone (TRH) analogue, were investigated in vivo and in vitro.

2. Rovatirelin orally administered to rats and dogs was rapidly absorbed and bioavailability was estimated to be 7.3 and 41.3%, respectively. The extent of plasma protein binding of rovatirelin in rats, dogs, and humans was low in all species (～15%). The permeability of rovatirelin from blood to brain (permeability-surface area) ranged from 1.04?±?0.14 to 1.29?±?0.28?μL/min/g in rats, and rovatirelin was stable in rat plasma and brain homogenates.

3. The metabolite pattern was qualitatively similar in vitro and in vivo. In animals, rovatirelin aminopentanoic acid (rovatirelin-acid), rovatirelin aminopentanone (rovatirelin-ketone), rovatirelin pyrrolidine (4S)-hydroxy (rovatirelin-OH), (thiazoylalanyl)methylpyrrolidine (TAMP), 3-(4-thiazoyl)-l-alanine (TA), and unknown metabolites were observed. In human hepatocytes, TAMP was mainly formed and no unique human metabolite was observed.

4. The radioactivity from administered [¹⁴C]rovatirelin was predominantly excreted in faeces in rats and dogs, and almost all radioactivity was recovered 168?h after administration. Absorption, brain penetration, and stability of rovatirelin in the brain were greater than for taltirelin.

5. Thus, orally administered rovatirelin is a potentially improved treatment for spinocerebellar degeneration compared with taltirelin.     

Analysis of thyroid hormone receptor betaA mRNA expression in Xenopus laevis tadpoles as a means to detect agonism and antagonism of thyroid hormone action

Amphibian metamorphosis represents a unique biological model to study thyroid hormone (TH) action in vivo. In this study, we examined the utility of thyroid hormone receptors alpha (TRalpha) and betaA (TRbetaA) mRNA expression patterns in Xenopus laevis tadpoles as molecular markers indicating modulation of TH action. During spontaneous metamorphosis, only moderate changes were evident for TRalpha gene expression whereas a marked up-regulation of TRbetaA mRNA occurred in hind limbs (prometamorphosis), head (late prometamorphosis), and tail tissue (metamorphic climax). Treatment of premetamorphic tadpoles with 1 nM 3,5,3'-triiodothyronine (T3) caused a rapid induction of TRbetaA mRNA in head and tail tissue within 6 to 12 h which was maintained for at least 72 h after initiation of T3 treatment. Developmental stage had a strong influence on the responsiveness of tadpole tissues to induce TRbetaA mRNA during 24 h treatment with thyroxine (0, 1, 5, 10 nM T4) or T3 (0, 1, 5, 10 nM). Premetamorphic tadpoles were highly sensitive in their response to T4 and T3 treatments, whereas sensitivity to TH was decreased in early prometamorphic tadpoles and strongly diminished in late prometamorphic tadpoles. To examine the utility of TRbetaA gene expression analysis for detection of agonistic and antagonistic effects on T3 action, mRNA expression was assessed in premetamorphic tadpoles after 48 h of treatment with the synthetic agonist GC-1 (0, 10, 50, 250 nM), the synthetic antagonist NH-3 (0, 40, 200, 1000 nM), and binary combinations of NH-3 (0, 40, 200, 1000 nM) and T3 (1 nM). All tested concentrations of GC-1 as well as the highest concentration of NH-3 caused an up-regulation of TRbetaA expression. Co-treatment with NH-3 and T3 revealed strong antagonistic effects by NH-3 on T3-induced TRbetaA mRNA up-regulation. Results of this study suggest that TRbetaA mRNA expression analysis could serve as a sensitive molecular testing approach to study effects of environmental compounds on the thyroid system in X. laevis tadpoles.     

Mode of action: developmental thyroid hormone insufficiency--neurological abnormalities resulting from exposure to propylthiouracil

Because thyroid hormone is essential for normal brain development before and after birth, environmental chemicals that interfere with thyroid hormone signaling can adversely affect brain development. Adverse consequences of thyroid hormone insufficiency depend both on severity and developmental timing, indicating that environmental antithyroid factors may produce different effects at different developmental windows of exposure. Mechanistic studies can provide important insight into the potential impact of chemicals on human thyroid function, but relevance to humans must be systematically evaluated. This kind of analysis depends on data sets that include information about animals and humans. The drug 6-n-propyl-2-thiouracil (PTU) is used in animals to experimentally manipulate serum thyroid hormone levels, and in humans to treat patients, including pregnant women, with Graves' disease. A systematic analysis of the mode of action (MOA) of PTU in rats and in humans discloses similar modes of action. While the analysis predicts that PTU doses that produce thyroid hormone insufficiency in humans would adversely affect the developing brain, careful monitoring of PTU administration in pregnant and lactating humans keeps infant serum thyroid hormone levels within the normal range.     

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.     

褐多孔菌水煎剂对肝硬化失代偿期的疗效观察

褐多孔菌(Polyporus picipes Fr)为担子菌纲,多孔菌目,多孔菌科。是寄生于多种倒木或腐木之非食用性真菌。该菌盛产于大小兴安岭林区,其药用价值,经近年临床验证,有活血化淤,改善心肌功能,益肾壮阳,强筋壮骨等功能。对治疗心脏病、关节炎、跌打损伤及阳萎等有显著疗效;经动物实验表明,该菌对小鼠巨噬细胞的吞噬功能及对溶菌酶的合成及释放均有明显的促进作用。提示其在抗感染及肿瘤的防治中将起重要作用。     

Endocrine active compounds affect thyrotropin and thyroid hormone levels in serum as well as endpoints of thyroid hormone action in liver, heart and kidney

To assess interference with endocrine regulation of the thyroid axis, rats (female, ovariectomised) were treated for 12 weeks with the suspected endocrine active compounds (EAC) or endocrine disrupters (ED) 4-nonylphenol (NP), octyl-methoxycinnamate (OMC) and 4-methylbenzylidene-camphor (4-MBC) as well as 17beta-estradiol (E2) and 5alpha-androstane-3beta,17beta-diol (Adiol) on the background of a soy-free or soy-containing diet, and endpoints relevant for regulation via the thyroid axis were measured. Thyrotropin (TSH) and thyroid hormone (T4, T3) serum levels were altered, but not in a way consistent with known mechanisms of feedback regulation of the thyroid axis. In the liver, malic enzyme (ME) activity was significantly increased by E2 and Adiol, slightly by OMC and MBC and decreased by soy, whereas type I 5'-deiodinase (5'DI) was decreased by all treatments. This may be due rather to the estrogenic effect of the ED, as there is no obvious correlation with T4 or T3 serum levels. None of the substances inhibited thyroid peroxidase (TPO) in vitro, except for NP. In general, several endocrine active compounds disrupt the endocrine feedback regulation of the thyroid axis. However, there was no uniform, obvious pattern in the effects of those ED tested, but each compound elicited its own spectrum of alterations, arguing for multiple targets of interference with the complex network of thyroid hormone action and metabolism.     

Pharmacological actions of thymol and an analogue at GABAB autoreceptors

GABA_B autoreceptors inhibit release of GABA from GABAergic nerve terminals. Agonists of these receptors (e.g. baclofen) inhibit, whereas antagonists (e.g. (+)‐(S)‐5,5‐dimethylmorpholinyl‐2‐acetic acid; Sch 50911) enhance release of the transmitter. The actions of thymol (2‐isopropyl‐5‐methylphenol) and the structurally related compound 2‐tert‐butyl‐4‐methylphenol, (4MP) on the release of [³H]‐GABA were examined in rat neocortical slices where the GABAergic nerves had been preloaded with [³H]‐GABA and subsequently stimulated electrically on two occasions (S₁ and S₂). Test agents, baclofen and Sch 50911 were added to the superfusion medium prior to the second period of stimulation (S₂). Stimulation‐induced overflow (SIO) of [³H]‐GABA as a consequence of these stimulations (SIO₁ and SIO₂) were calculated and the effects of agents determined by comparing the SIO₂/SIO₁ ratio in the presence of each agent with that in control tissue. Thymol potentiated the release of [³H]‐GABA (EC₅₀ 170 μmol/L), an action reversed by baclofen (2 μmol/L). Baclofen alone had little effect on GABA release. Release of [³H]‐GABA was inhibited by 4MP (IC₅₀ 3 μmol/L) and this effect was blocked by Sch 50911 (10 μmol/L). Alone, Sch 50911 markedly potentiated the release of GABA. These results imply that 4MP is an agonist of GABA_B autoreceptors; however, further studies are needed to confirm that thymol is indeed a GABA_B autoreceptor antagonist. Of interest are structural differences in these agents. Thymol has a propyl group in the ortho position relative to the phenolic hydroxyl, whereas in 4MP this is a butyl group and the methyl group moves from position 5 to 4. Whether one or both of these changes was responsible for the above actions is unknown.     

Mitochondrial F(0) F(1) -ATP synthase is a molecular target of 3-iodothyronamine, an endogenous metabolite of thyroid hormone

BACKGROUND AND PURPOSE

3-iodothyronamine (T1AM) is a metabolite of thyroid hormone acting as a signalling molecule via non-genomic effectors and can reach intracellular targets. Because of the importance of mitochondrial F₀F₁-ATP synthase as a drug target, here we evaluated interactions of T1AM with this enzyme.

EXPERIMENTAL APPROACH

Kinetic analyses were performed on F₀F₁-ATP synthase in sub-mitochondrial particles and soluble F₁-ATPase. Activity assays and immunodetection of the inhibitor protein IF₁ were used and combined with molecular docking analyses. Effects of T1AM on H9c2 cardiomyocytes were measured by in situ respirometric analysis.

KEY RESULTS

T1AM was a non-competitive inhibitor of F₀F₁-ATP synthase whose binding was mutually exclusive with that of the inhibitors IF₁ and aurovertin B. Both kinetic and docking analyses were consistent with two different binding sites for T1AM. At low nanomolar concentrations, T1AM bound to a high-affinity region most likely located within the IF₁ binding site, causing IF₁ release. At higher concentrations, T1AM bound to a low affinity-region probably located within the aurovertin binding cavity and inhibited enzyme activity. Low nanomolar concentrations of T1AM increased ADP-stimulated mitochondrial respiration in cardiomyocytes, indicating activation of F₀F₁-ATP synthase consistent with displacement of endogenous IF_1,, reinforcing the in vitro results.

CONCLUSIONS AND IMPLICATIONS

Effects of T1AM on F₀F₁-ATP synthase were twofold: IF₁ displacement and enzyme inhibition. By targeting F₀F₁-ATP synthase within mitochondria, T1AM might affect cell bioenergetics with a positive effect on mitochondrial energy production at low, endogenous, concentrations. T1AM putative binding locations overlapping with IF₁ and aurovertin binding sites are described.     

The anti-nausea effects of CB1 agonists are mediated by an action at the visceral insular cortex

BACKGROUND AND PURPOSE

Conditioned gaping reactions reflect nausea-induced behaviour in rats. Cannabinoid 1 receptor (CB₁) agonists interfere with the establishment of nausea-induced conditioned gaping; however, it is not known if their effects are mediated by an action at peripheral or central CB₁ receptors.

EXPERIMENTAL APPROACH

We utilized the conditioned gaping model of nausea to evaluate the effect of peripheral and central administration of the peripherally restricted CB₁ agonist, CB13, on the establishment of LiCl-induced gaping in rats. We further evaluated the ability of HU-210 administered to the gustatory insular cortex (GIC) or visceral insular cortex (VIC) to interfere with LiCl-induced conditioned gaping and determined if this effect was mediated by CB₁ receptors.

KEY RESULTS

Central, but not peripheral, CB13 suppressed LiCl-induced conditioned gaping. Central administration of the potent CB₁ agonist, HU-210, delivered to the VIC, but not the GIC, suppressed the establishment of LiCl-induced gaping reactions, but not LiCl-induced suppression of hedonic reactions or conditioned taste avoidance. This pattern of results suggests that HU-210 delivered to the VIC prevented LiCl-induced nausea, but not learning per se. The suppression of LiCl-induced conditioned gaping by HU-210 was mediated by CB₁ receptors because it was prevented by co-administration of CB₁ antagonist/inverse agonist, AM-251, into the VIC. A high dose of AM-251 (20 µg) administered alone into the VIC did not produce conditioned gaping reactions.

CONCLUSIONS AND IMPLICATIONS

The nausea-relieving effects of CB₁ agonists, but not the nausea-inducing effects of CB₁ inverse agonists, are mediated, at least in part, by their action at the VIC in rats.     

Characteristics of hydrocortisone action on the biosynthesis of mitochondrial and cytoplasmic RNA in rat liver cells at different thyroid hormone levels in the body

Hydrocortisone effect on RNA synthesis was shown to depend on thyroid hormone levels: the inducing action of hydrocortisone on RNA synthesis in liver mitochondria was revealed only in intact and triiodothyronine-treated thyroidectomized rats. In hypothyrosis hydrocortisone failed to produce a significant change in intensity of mitochondrial and cytoplasmic RNA synthesis.     

The roles of aldo-keto reductases in steroid hormone action

The human aldo-keto reductase 1C (AKR1C) isozymes are implicated in the pre-receptor regulation of steroid receptors, nuclear orphan receptors and membrane-bound ligand-gated ion channels. Human AKR members that may regulate the local concentration of steroid hormones include: AKR1C1, AKR1C2, AKR1C3, AKR1C4 and AKR1D1. Since, these enzymes are pluripotent, the physiological role for the human AKR1C isozymes is determined by their tissue-specific expression patterns and their substrate availability in target tissues. AKRs work in concert with short-chain dehydrogenases/reductases as switches to control ligand access to nuclear receptors. Consequently, they are potential targets in treating prostate cancer, breast cancer, endometriosis and endometrial cancer.     

Depolarizing action of neostigmine at an autonomic ganglion

The actions of neostigmine have been examined using electrical recording from normal and denervated superior cervical ganglia from rat and kitten. Neostigmine produced a rapid and reversible depolarization of the ganglion cells, both in vitro and in vivo. This depolarization could be antagonized by hexamethonium, and was not related to an anticholinesterase action. Eserine blocked transmission and only produced a small depolarization of slow onset and development. This depolarization was reversible, but could not be antagonized by hexamethonium.     

The depressant action of morphine on transmission at a skeletal neuromuscular junction is non-specific

The depressant actions of apomorphine, etorphine, dextromoramide, laevomoramide, naloxone, codeine, morphine and nalorphine have been examined on the rat diaphragm preparation. Their descending order of potency (in the order given above) differed greatly from that published for activity at specific opiate receptors. The depressant action of morphine was not antagonized by naloxone. The stereoisomers dextro- and laevomoramide were equipotent in depressing the preparation. On the transmurally stimulated guinea-pig ileum preparation the depressant action of dextromoramide was antagonized by naloxone. Laevomoramide was 10 000 times less potent than its (+)-isomer, and was not antagonized by naloxone. It is concluded that the effects of narcotic analgesics on transmission at a skeletal neuromuscular junction are not mediated via opiate receptors.     

氟斑牙儿童甲状腺激素异常与DIO1基因多态性的关系

目的　分析氟斑牙儿童甲状腺激素异常情况及与Ⅰ型脱碘酶（DIO1）基因多态性的关系。方法　2018年6月—2019年6月,在天津市历史水氟区和非水氟区共随机抽取169名7~12岁儿童,检测儿童氟斑牙水平。其中正常儿童（正常组）79名,氟斑牙儿童（氟斑牙组）90名。采集尿样,利用砷铈催化分光光度方法测定尿碘水平。采集血样,化学发光法检测促甲状腺激素（TSH）、游离三碘甲状腺原氨酸（FT3）和游离甲状腺素（FT4）,采用Sequenom SNP分型检测实验测定DIO1中rs2294512位点的多态性,并进行问卷调查。根据DIO1 rs2294512位点的基因型分层后进行多因素Logistic回归分析,研究DIO1基因多态性在氟斑牙与甲状腺激素异常中的作用。结果　相对于正常组,氟斑牙组FT3水平较高,FT4水平较低（P＜0.05）。氟斑牙组FT3过高率达40.0%,高于正常组的21.5%,FT4过高率为3.3%,低于正常组的12.7%（P＜0.05）。DIO1基因AA基因型儿童中,患氟斑牙者FT3较高（OR=6.357,95%CI：1.808~22.347,P=0.004）。结论　DIO1基因rs2294512位点为AA基因型的氟斑牙儿童FT3水平更易升高。     

Thyroid hormone receptor isoform selectivity of thyroid hormone disrupting compounds quantified with an in vitro reporter gene assay

Some compounds, including brominated diphenyl ethers (BDEs), can interfere with thyroid hormone (TH) receptor (TR)-mediated TH-signalling. In this study, the TR isoform selectivity of some TH disrupting compounds was investigated with TR/β specific reporter gene assays. For this purpose, the effects of compounds on 3,3′,5-triiodothyronine (T₃)-induced TR- or TRβ-activation were tested in green monkey kidney fibroblast (CV-1) cells transiently transfected with Xenopus TRs and a luciferase reporter gene. The T₃-like BDE-OH and diiodobiphenyl (DIB) increased T₃-induced TR-activation, but not T₃-induced TRβ-activation. BDE28 (100 nM) did not act via TR, but almost tripled T₃-induced TRβ-activation relative to T₃ at its EC₅₀. BDE206 (100 nM) was antagonistic on both TRs with a maximum repression −54% relative to T₃ at its EC₅₀. Contrary to previous results obtained with the T-screen, HBCD was inactive. The present study illustrates the importance of testing potential TH disrupting compounds in model systems that enable independent characterization of effects on both T₃-induced TRs.