Thyroxine-binding Globulin Research Articles

6784 A Case of Euthyroid Hyperthyroxinemia due to Thyroid Binding Globulin Excess Syndrome

Abstract Disclosure: A.S. Iyer: None. Background: Congenital thyroid binding globulin (TBG) excess is a rare phenomenon associated with elevated serum total T3 and total T4 concentrations but normal serum concentrations of free thyroid hormones, with clinically euthyroid patients. While TBG excess can be caused by pregnancy, estrogen-secreting tumors, and estrogen therapy, congenital TBG excess follows an X-linked pattern, with hemizygous males most affected, and heterozygous females showing a spectrum of disease due to random inactivation of one X chromosome. Clinical Case: A 39-year-old Caucasian female presented as a referral from the Gastroenterology clinic due to concern for thyroid resistance syndrome. Symptoms included chronic constipation (improving with Miralax®), gradual weight gain of 8 pounds in one year, fatigue, and palpitations. She reported that her total thyroid hormone levels have always been elevated, with other thyroid labs remaining within normal limits, along with family history of similar labs noted in her two sons, father, and paternal grandmother. Upon initial encounter, TSH was 1.637 (0.430-3.550 uIU/mL), total T4 15.4 (4.8-11.7 ug/dL), total T3 231 (80-200 ng/dL), free T4 0.97 (0.70-1.25 ng/dL), free T3 3.2 (1.7-3.7 pg/mL), and albumin 4.2 (3.5-5.0 g/dL). The patient was not on oral contraceptive pills and she denied any pregnancies in the last three years. Thyroid ultrasound showed a normal-appearing homogeneous thyroid gland with a small cyst with colloid and no cervical lymphadenopathy. Initial differential diagnosis included TBG excess syndrome versus familial dysalbuminemic hyperthyroxinemia. Permission was obtained from the patient to access one of her son’s medical records from age 8-weeks old when he was also evaluated for abnormal thyroid labs. TSH was 2.144 (0.350-6.500 uIU/mL), total T4 28.2 (5.0-12.0 ug/dL), free T4 1.55 (0.8-1.8 ng/dL), and free T3 4.0 pg/mL (no reference available). Thyroid binding globulin was found to be elevated at 81 (12-26 mcg/mL) in her son and found to be elevated to 78.0 (13.5-30.9 mcg/mL) in this patient, confirming a diagnosis of TBG excess syndrome. Conclusions: TBG excess syndrome should be considered in the differential of patients with high total T3 and total T4 levels with normal levels of free T3, free T4, and TSH, especially in individuals who have a known family history and who have minimal or nonspecific symptoms. Definitive diagnosis will make further testing and treatment unnecessary. However, if these patients develop hypo- or hyperthyroidism, then use of TSH and free levels of T4 and T3 is necessary to direct management and avoid confusion. Reference: Pappa, T., and S. Refetoff. “Thyroid hormone transport proteins: Thyroxine-binding globulin, transthyretin, and albumin.” Reference Module in Neuroscience and Biobehavioral Psychology, 2017, https://doi.org/10.1016/b978-0-12-809324-5.03494-5. Presentation: 6/2/2024

7915 A Case of Severe Hypothyroidism in a Patient with Nephrotic Syndrome presenting with Rhabdomyolysis requiring Levothyroxine and Liothyronine combination therapy

Abstract Disclosure: S.S. Mohammed: None. E.T. Ngo: None. S. Tadisina: None. B.M. Drees: None. Background: Nephrotic syndrome is known to worsen hypothyroidism via urinary loss of thyroid binding globulin, transthyretin, albumin and other proteins, often requiring escalating levothyroxine doses. Severe uncontrolled hypothyroidism can result in rhabdomyolysis, although this presentation is quite rare. Clinical case: We present a case of a 50-year-old male with long-standing Hashimoto’s hypothyroidism, biopsy-proven minimal change disease with nephrotic syndrome, dyslipidemia, and hypertension, who was admitted for generalized myalgia, weakness, and progressive swelling of bilateral hands and feet for one month. He had been off levothyroxine 3 months prior to presentation. He previously required large doses of oral levothyroxine, as high as 350mcg daily, but never achieved a euthyroid state despite reported adherence to therapy with the high levothyroxine doses.Laboratory workup showed severe hypothyroidism (free thyroxine <0.25ng/dL [0.6-1.6ng/dL] with markedly elevated thyroid stimulating hormone 282.03 mIU/mL [0.3-5.6mIU/mL]), along with acute kidney injury and rhabdomyolysis (Creatine kinase 4882 U/L[38-234U/L]). He was hemodynamically stable with intact mentation and was not deemed to be in myxedema coma. Physical examination was consistent with hypothyroidism with periorbital swelling, dry skin, deep hoarse voice, bilateral hand and feet edema, and delayed deep tendon reflexes. Thyroid function tests and clinical symptoms failed to improve after 8 days, despite high doses of levothyroxine IV (200mcg). Creatine kinase remained high at 4994 U/L [38-234U/L] despite adequate fluid hydration. Liothyronine 5mcg orally was started in addition to levothyroxine 200mcg IV. Repeat thyroid function tests after 2 days of combined IV levothyroxine and oral liothyronine therapy showed significant downtrend in TSH to 154.12 uIU/ml [0.3-5.6mIU/mL] and increase in free thyroxine to 0.44ng/dl [0.6-1.6ng/dL]. Creatine kinase also down trended to 3181U/L[38-234U/L] on D4 of IV levothyroxine 200mcg IV with liothyronine 5mcg daily. He was discharged stable and clinically improved on oral levothyroxine and liothyronine. Laboratory evaluation 10 days later showed further improvement in TFTs (TSH 66.0[0.3-5.6mIU/mL]), free thyroxine 0.6 [0.6-1.6ng/dL] Conclusion: This case presents a unique and unusual clinical course in symptomatic primary hypothyroidism with rhabdomyolysis and AKI. Rhabdomyolysis due to hypothyroidism, without an obvious precipitating factor, has been previously reported, but is very rare. There is limited evidence regarding combination treatment with levothyroxine and liothyronine in primary hypothyroidism; however, as demonstrated in this patient, combination therapy resulted in clinical and biochemical improvement of thyroid function. Presentation: 6/2/2024

9396 Deciphering The Enigma: A Case Report On New-onset Graves Disease Presenting As Thyroid Storm In The First Trimester Of Pregnancy, Managed In The Intensive Care Setting

Abstract Disclosure: M. Zeb: None. S.W. Salari: None. A. Tiwari: None. A. Vadher: None. A. Dabaja: None. S. Kambhatla: None. Graves' disease, an autoimmune disorder characterized by hyperthyroidism, presents unique challenges when manifesting as thyroid storm during pregnancy. We report a case of a 27-year-old African American woman at 9 weeks gestation who presented with palpitations, agitation, and fever. On examination, she exhibited fever, tachycardia, tremors in hands, and mild bilateral exophthalmos. Thyroid function tests revealed markedly elevated free thyroxine and suppressed thyroid-stimulating hormone levels. Thyroid ultrasound confirmed diffuse thyroid enlargement with increased vascularity, consistent with Graves' disease. Pelvic ultrasound estimated the gestational age at 9 weeks and 2 days, with a serum β-hCG level of 135,037 mIU/mL. An electrocardiogram revealed sinus tachycardia, and a complete metabolic panel indicated mild hypokalemia. The Thyroid Stimulation Immunoglobulin (TSI) and Thyrotropin receptor antibodies were tested positive. The Burch-Warsofsky point score of 45, supported the diagnosis of thyroid storm. The patient received intensive care treatment including intravenous fluids, hydrocortisone, beta-blockers, Lugol’s iodine, propylthiouracil, and potassium replacement. Following treatment, thyroid function stabilized within 48 hours, and her hyperthyroid symptoms resolved. The patient was discharged on oral labetalol and propylthiouracil. Thyroid storm, characterized by severe manifestations of hyperthyroidism, is a rare but potentially life-threatening condition, especially during pregnancy. Prompt recognition and intervention are crucial due to associated maternal and fetal morbidity and mortality. A multidisciplinary approach, involving endocrinology, obstetrics, and critical care, is essential to optimize outcomes. The unique physiologic changes of pregnancy, such as increased thyroid hormone production and altered thyroid hormone-binding globulin levels, can complicate the diagnosis and management of hyperthyroidism. Our case underscores the importance of vigilance for thyroid dysfunction in pregnant women, even in the absence of prior thyroid disease. Additionally, the potential impact of hyperthyroidism and thyroid storm on pregnancy outcomes highlights the need for early recognition and intervention. Long-term management of Graves' disease during pregnancy may also require adjustment of antithyroid medication dosage and monitoring of thyroid function to maintain euthyroidism while minimizing fetal exposure to medication. Further research is warranted to refine diagnostic criteria, treatment protocols, and long-term management strategies for thyroid storm in pregnancy. Increased awareness among healthcare providers about the risks and management strategies for this rare but serious complication is also necessary. Presentation: 6/3/2024

Association between serum levels of 4-tertiary-octylphenol and thyroid function in a young cohort study

4-tertiary-octylphenol (4-t-OP) is a commonly used alkylphenol present in a variety of consumer products. Earlier experimental investigations have suggested that 4-t-OP leads to thyroid dysfunction. However, it is unclear whether these effects translate to humans. We recruited 886 adolescents and young adults (aged 12–30 years) from Taiwan and explored the associations between serum levels of 4-t-OP and various thyroid panel parameters including free and total thyroxine (T4) and triiodothyronine (T3), thyroid-stimulating hormone (TSH), and thyroxine-binding globulin (TBG). Our findings indicated that a one-unit increase in the natural logarithm (ln) of 4-t-OP levels was positively associated with both total T3 and ln free T4, with β values of 3.122 (SE = 1.400, P = 0.026) and 0.046 (SE = 0.015, P = 0.002), respectively. Furthermore, we observed a statistically significant upward trend in the mean values of total T3 and ln free T4 as the quartiles of 4-t-OP exposure increased (P for trend = 0.001 and 0.025, respectively). Nevertheless, our analysis did not uncover any differences in the odds ratio of thyroid diseases based on exposure to 4-t-OP in the logistic regression analysis. In conclusion, our study reveals an association between serum concentrations of 4-t-OP and biomarkers of thyroid function. However, these effects may manifest as subclinical. Further investigations are essential to establish a causal relationship between 4-t-OP exposure and thyroid function in human subjects.

In Vitro Screening for ToxCast Chemicals Binding to Thyroxine-Binding Globulin.

Thyroid hormone (TH) carrier proteins play an important role in distributing TH to target tissue as well as maintaining the balance of free versus bound TH in the blood. Interference with the TH carrier proteins has been identified as a potential mechanism of thyroid system disruption. To address the lack of data regarding chemicals binding to these carrier proteins and displacing TH, a fluorescence-based in vitro screening assay was utilized to screen over 1,400 chemicals from the U.S. EPA's ToxCast phase1_v2, phase 2, and e1k libraries for competitive binding to one of the carrier proteins, thyroxine-binding globulin. Initial screening at a single high concentration of 100 μM identified 714 chemicals that decreased signal of the bound fluorescent ligand by 20% or higher. Of these, 297 produced 50% or greater reduction in fluorescence and were further tested in concentration-response (0.004 to 150 μM) to determine relative potency. Ten chemicals were found to have EC50 values <1 μM, 63 < 10 μM, and 141 chemicals between 10 and 100 μM. Utilization of this assay contributes to expanding the number of in vitro assays available for identifying chemicals with the potential to disrupt TH homeostasis. These results support ranking and prioritization of chemicals to be tested in vivo to aid in the development of a framework for predicting in vivo effects from in vitro high-throughput data.

Induced Muscle and Liver Absence of Gne in Postnatal Mice Does Not Result in Structural or Functional Muscle Impairment.

GNE Myopathy is a unique recessive neuromuscular disorder characterized by adult-onset, slowly progressive distal and proximal muscle weakness, caused by mutations in the GNE gene which is a key enzyme in the biosynthesis of sialic acid. To date, the precise pathophysiology of the disease is not well understood and no reliable animal model is available. Gne KO is embryonically lethal in mice. To gain insights into GNE function in muscle, we have generated an inducible muscle Gne KO mouse. To minimize the contribution of the liver to the availability of sialic acid to muscle via the serum, we have also induced combined Gne KO in liver and muscle. A mouse carrying loxp sequences flanking Gne exon3 was generated by Crispr/Cas9 and bred with a human skeletal actin (HSA) promoter driven CreERT mouse. Gne muscle knock out was induced by tamoxifen injection of the resulting homozygote GneloxpEx3loxp/HSA Cre mouse. Liver Gne KO was induced by systemic injection of AAV8 vectors carrying the Cre gene driven by the hepatic specific promoter of the thyroxine binding globulin gene. Characterization of these mice for a 12 months period showed no significant changes in their general behaviour, motor performance, muscle mass and structure in spite of a dramatic reduction in sialic acid content in both muscle and liver. We conclude that post weaning lack of Gne and sialic acid in muscle and liver have no pathologic effect in adult mice. These findings could reflect a strong interspecies versatility, but also raise questions about the loss of function hypothesis in Gne Myopathy. If these findings apply to humans they have a major impact on therapeutic strategies.

Targeting PYK2 with heterobifunctional T6BP helps mitigate MASLD and MASH-HCC progression

Background & AimsThe mechanisms underlying the regulation of hepatocyte non-receptor tyrosine kinases in metabolic dysfunction-associated steatohepatitis (MASH) remain largely unclear. MethodsHepatocyte-specific overexpression or deletion and anti-protein tyrosine kinase 2 beta (PYK2) or anti-TRAF6-binding protein (T6BP) crosslinking were utilised to study fatty liver protection by T6BP. P-PTC, a peptide-proteolysis targeting chimaera, degrades PYK2 to block MASH progression. ResultsSince PYK2 activation is promoter signalling in steatohepatitis development, we find that T6BP is a novel and critical suppressor of PYK2 that reduces hepatic lipid accumulation, pro-inflammatory factor release, and pro-fibrosis production by ubiquitin ligase CBL to degrade PYK2. Mechanistic evidence suggests that T6BP directly targets PYK2 and prevents its N-terminal FERM domain-triggered dimerization, disrupting downstream PYK2-JNK signalling hyperactivation. Additionally, T6BP favourably recruits CBL, a particular E3 ubiquitin ligase targeting PYK2, to form a complex and degrade PYK2. T6BP (F1), a core fragment of T6BP, directly blocks N-terminal FERM domain-associated dimerization of PYK2, followed by T6BP-recruiting CBL-mediated PYK2 degradation in a typical T6BP-dependent manner when the tiny fragment is specifically expressed using thyroxine binding globulin (TBG)-ground vectors. This inhibits the progression of MASH, metabolic dysfunction-associated steatotic liver disease (MASLD)-related HCC (MASH-HCC), and metabolic syndrome in dietary rodent models. First-ever peptide-proteolysis targeting chimaera (P-PTC) based on the core segment of T6BP as a ligand for targeted recruitment of CBL targeting metabolic disorders like MASH has been devised and validated in animal models. ConclusionsOur study revealed a previously unknown mechanism: identification of T6BP as a key eliminator of fatty liver strongly contributes to the development of promising therapeutic targets, and the discovery of crucial fragments of T6BP-based pharmacon that interrupt PYK2 dimerization are novel and viable treatments for fatty liver and its advanced symptoms and complications. Impact and implicationsExcessive high-energy diet ingestion is critical in driving steatohepatitis via regulation of hepatocyte non-receptor tyrosine kinases. The mechanisms under lying the regulation of hepatocyte PYK2 in metabolic dysfunction-associated steatohepatitis (MASH) remain largely unclear. Here, we found that T6BP as a critical fatty liver eliminator has a significant impact on the development of promising therapeutic targets. Additionally, vital T6BP-based pharmacon fragments that impede PYK2 dimerization have been found, offering new and effective treatments for advanced fatty liver symptoms and complications.

Optimized methods for measuring competitive binding of chemical substances to thyroid hormone distributor proteins transthyretin and thyroxine binding globulin

Transthyretin (TTR) and thyroxine-binding globulin (TBG) are two major thyroid hormone (TH) distributor proteins in human plasma, playing important roles in stabilizing the TH levels in plasma, delivery of TH to target tissues, and trans-barrier transport. Binding of xenobiotics to these distributor proteins can potentially affect all these three important roles of distributor proteins. Therefore, fast and cost-effective experimental methods are required for both TTR and TBG to screen both existing and new chemicals for their potential binding. In the present study, the TTR-binding assay was therefore simplified, optimized and pre-validated, while a new TBG-binding assay was developed based on fluorescence polarization as a readout. Seven model compounds (including positive and negative controls) were tested in the pre-validation study of the optimized TTR-binding assay and in the newly developed TBG-binding assay. The dissociation constants of the natural ligand (thyroxine, T4) and potential competitors were determined and compared between two distributor proteins, showing striking differences for perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA).

Longitudinal proteomics of leptin treatment in humans with acute and chronic energy deficiency-induced hypoleptinemia reveal novel, mainly immune-related, pleiotropic effects

BackgroundLeptin is known for its metabolic, immunomodulatory and neuroendocrine properties, but the full spectrum of molecules downstream of leptin and relevant underlying mechanisms remain to be fully clarified. Our objective was to identify proteins and pathways influenced by leptin through untargeted proteomics in two clinical trials involving leptin administration in lean individuals. MethodsWe performed untargeted liquid chromatography-tandem mass spectrometry serum proteomics across two studies a) Short-term randomized controlled crossover study of lean male and female humans undergoing a 72-h fast with concurrent administration of either placebo or high-dose leptin; b) Long-term (36-week) randomized controlled trial of leptin replacement therapy in human females with acquired relative energy deficiency and hypoleptinemia. We explored longitudinal proteomic changes and run adjusted mixed models followed by post-hoc tests. We further attempted to identify ontological pathways modulated during each experimental condition and/or comparison, through integrated qualitative pathway and enrichment analyses. We also explored dynamic longitudinal relationships between the circulating proteome with clinical and hormonal outcomes. Results289 and 357 unique proteins were identified per each respective study. Short-term leptin administration during fasting markedly upregulated several proinflammatory molecules, notably C-reactive protein (CRP) and cluster of differentiation (CD) 14, and downregulated lecithin cholesterol acyltransferase and several immunoglobulin variable chains, in contrast with placebo, which produced minimal changes. Quantitative pathway enrichment further indicated an upregulation of the acute phase response and downregulation of immunoglobulin- and B cell-mediated immunity by leptin. These changes were independent of participants' biological sex. In the long term study, leptin likewise robustly and persistently upregulated proteins of the acute phase response, and downregulated immunoglobulin-mediated immunity. Leptin also significantly and differentially affected a wide array of proteins related to immune function, defense response, coagulation, and inflammation compared with placebo. These changes were more notable at the 24-week visit, coinciding with the highest measured levels of serum leptin. We further identified distinct co-regulated clusters of proteins and clinical features during leptin administration indicating robust longitudinal correlations between the regulation of immunoglobulins, immune-related molecules, serpins (including cortisol and thyroxine-binding globulins), lipid transport molecules and growth factors, in contrast with placebo, which did not produce similar associations. ConclusionsThese high-throughput longitudinal results provide unique functional insights into leptin physiology, and pave the way for affinity-based proteomic analyses measuring several thousands of molecules, that will confirm these data and may fully delineate underlying mechanisms.

Preclinical evaluation of tissue-selective gene therapies for congenital generalised lipodystrophy

Lipodystrophy is a rare disorder which can be life-threatening. Here individuals fail to develop or maintain appropriate adipose tissue stores. This typically causes severe metabolic complications, including hepatic steatosis and lipoatrophic diabetes. There is no cure for lipodystrophy, and treatment options remain very limited. Here we evaluate whether tissue-selective adeno-associated virus (AAV) vectors can provide a targeted form of gene therapy for lipodystrophy, using a preclinical lipodystrophic mouse model of Bscl2 deficiency. We designed AAV vectors containing the mini/aP2 or thyroxine-binding globulin promoter to selectively target adipose or liver respectively. The AAV-aP2 vectors also contained the liver-specific microRNA-122 target sequence, restricting hepatic transgene expression. Systemic delivery of AAV-aP2 vectors overexpressing human BSCL2 restored adipose tissue development and metabolic health in lipodystrophic mice without detectable expression in the liver. High doses (1 × 1012 GCs) of liver-selective vectors led to off target expression and adipose tissue development, whilst low doses (1 × 1010 GCs) expressed selectively and robustly in the liver but did not improve metabolic health. This reveals that adipose tissue-selective, but not liver directed, AAV-mediated gene therapy is sufficient to substantially recover metabolic health in generalised lipodystrophy. This provides an exciting potential new avenue for an effective, targeted, and thereby safer therapeutic intervention.

Hepatic LRP-1 plays an important role in amyloidosis in Alzheimer's disease mice: Potential role in chronic heavy alcohol feeding

BackgroundHepatic lipoprotein receptor-related protein 1 (LRP-1) plays a central role in peripheral amyloid beta (Aβ) clearance, but its importance in Alzheimer's disease (AD) pathology is understudied. Our previous work showed that intragastric alcohol feeding to C57BL/6 J mice reduced hepatic LRP-1 expression which correlated with significant AD-relevant brain changes. Herein, we examined the role of hepatic LRP-1 in AD pathogenesis in APP/PS1 AD mice using two approaches to modulate hepatic LRP-1, intragastric alcohol feeding to model chronic heavy drinking shown by us to reduce hepatic LRP-1, and hepato-specific LRP-1 silencing. MethodsEight-month-old male APP/PS1 mice were fed ethanol or control diet intragastrically for 5 weeks (n = 7–11/group). Brain and liver Aβ were assessed using immunoassays. Three important mechanisms of brain amyloidosis were investigated: hepatic LRP-1 (major peripheral Aβ regulator), blood-brain barrier (BBB) function (vascular Aβ regulator), and microglia (major brain Aβ regulator) using immunoassays. Spatial LRP-1 gene expression in the periportal versus pericentral hepatic regions was confirmed using NanoString GeoMx Digital Spatial Profiler. Further, hepatic LRP-1 was silenced by injecting LRP-1 microRNA delivered by the adeno-associated virus 8 (AAV8) and the hepato-specific thyroxine-binding globulin (TBG) promoter to 4-month-old male APP/PS1 mice (n = 6). Control male APP/PS1 mice received control AAV8 (n = 6). Spatial memory and locomotion were assessed 12 weeks after LRP-1 silencing using Y-maze and open-field test, respectively, and brain and liver Aβ were measured. ResultsAlcohol feeding reduced plaque-associated microglia in APP/PS1 mice brains and increased aggregated Aβ (p < 0.05) by ELISA and 6E10-positive Aβ load by immunostaining (p < 0.05). Increased brain Aβ corresponded with a significant downregulation of hepatic LRP-1 (p < 0.01) at the protein and transcript level, primarily in pericentral hepatocytes (zone 3) where alcohol-induced injury occurs. Hepato-specific LRP-1 silencing significantly increased brain Aβ and locomotion hyperactivity (p < 0.05) in APP/PS1 mice. ConclusionChronic heavy alcohol intake reduced hepatic LRP-1 expression and increased brain Aβ. The hepato-specific LRP-1 silencing similarly increased brain Aβ which was associated with behavioral deficits in APP/PS1 mice. Collectively, our results suggest that hepatic LRP-1 is a key regulator of brain amyloidosis in alcohol-dependent AD.

An in silico study on human carcinogenicity mechanism of polybrominated biphenyls exposure

Polybrominated biphenyls (PBBs) are associated with an increased risk of thyroid cancer; however, relevant mechanistic studies are lacking. In this study, we investigated the mechanisms underlying PBB-induced human thyroid cancer. Molecular docking and molecular dynamics methods were employed to investigate the metabolism of PBBs by the cytochrome P450 enzyme under aryl hydrocarbon receptor mediation into mono- and di-hydroxylated metabolites. This was taken as the molecular initiation event. Subsequently, considering the interactions of PBBs and their metabolites with the thyroxine-binding globulin protein as key events, an adverse outcome pathway for thyroid cancer caused by PBBs exposure was constructed. Based on 2D quantitative structure activity relationship (2D-QSAR) models, the contribution of amino acid residues and binding energy were analyzed to understand the mechanism underlying human carcinogenicity (adverse effect) of PBBs. Hydrogen bond and van der Waals interactions were identified as key factors influencing the carcinogenic adverse outcome pathway of PBBs. Analysis of non-bonding forces revealed that PBBs and their hydroxylation products were predominantly bound to the thyroxine-binding globulin protein through hydrophobic and hydrogen bond interactions. The key amino acids involved in hydrophobic interactions were alanine 330, arginine 381 and lysine 270, and the key amino acids involved in hydrogen bond interactions were arginine 381 and lysine 270. This study provides valuable insights into the mechanisms underlying human health risk associated with PBBs exposure.

#1246 The impact of severe nephrotic syndrome on thyroid function

Abstract Background and Aims Nephrotic syndrome (NS) is a clinical condition characterized by massive urinary loss of proteins, mostly albumin, but also hormones and their carrier proteins among others. The most frequently reported hormonal complication is thyroid dysfunction. The study aimed to assess the frequency of thyroid dysfunction in NS and its association with carrier protein levels and indicators of disease severity. Method A case-control study was conducted involving patients with newly diagnosed or relapsed severe NS, defined as proteinuria &amp;gt; 3.5 g/day and serum albumin ≤ 2.5 g/dL (NS group), and patients without proteinuria (control group). The evaluation included thyroid hormone profiles, serum levels of carrier proteins (prealbumin – PAB, and thyroid-binding globulin – TBG), and markers reflecting the course of NS. Results Forty-two nephrotic and 40 matched non-proteinuric patients were enrolled. The NS group comprised 67% males with a mean age of 49 years and an average proteinuria of 8.9 g/day (Table 1). The leading cause of NS was minimal change disease (22 patients), followed by membranous nephropathy (11 patients). The other causes included: amyloidosis (3 patients: AL – 2 cases, A – 1 case), focal segmental glomerulosclerosis (2 patients) and lupus nephritis (1 case). In 5 cases, no histological diagnosis was made. Thyroid dysfunction secondary to NS was observed in the majority of patients, occurring 18-times more frequently than in the control group (67% vs 10%, OR = 18, 95% CI: 5.3-60.7). Euthyroid sick syndrome was the most commonly seen in NS (15 cases, 36%), followed by overt (8 cases, 19%) and subclinical hypothyroidism (5 cases, 12%). According to the current guidelines, levothyroxine supplementation was required in 11 patients (26% of the NS group, 36% of those with thyroid dysfunction). Serum TSH correlated inversely with PAB (R = −0.63, p &amp;lt; 0.001), and positively with TBG (R = 0.39, p = 0.010), while no relationships were found between carrier proteins and free hormones (fT3 or fT4). The only indicator of NS severity related to thyroid function was serum albumin. It correlated, however, only with TSH (R = −0.41, p = 0.007), not with free hormones. Additionally, neither histological type, nor clinical course of NS distinguished between euthyroidism, euthyroid sick syndrome, or hypothyroidism (Table 2). Conclusion Thyroid dysfunction is a common complication of severe NS. Although euthyroid sick syndrome predominates, the proportion of patients with hypothyroidism who may potentially require levothyroxine replacement therapy remains substantial.

Liquid crystal monomers disrupt photoreceptor patterning of zebrafish larvae via thyroid hormone signaling

Liquid crystal monomers (LCMs) are the raw material for liquid crystal displays, and their use is steadily increasing in electronic products. Recently, LCMs have been reported to be novel endocrine disrupting chemicals, however, the mechanisms underlying their potential for thyroid hormone disruption and visual toxicity are not well understood. In this study, six widely used fluorinated LCMs (FLCMs) were selected to determine putative mechanisms underlying FLCM-induced toxicity to the zebrafish thyroid and visual systems. Exposure to FLCMs caused damage to retinal structures and reduced cell density of ganglion cell layer, inner nuclear layer, and photoreceptor layer approximately 12.6–46.1%. Exposure to FLCMs also disrupted thyroid hormone levels and perturbed the hypothalamic-pituitary-thyroid axis by affecting key enzymes and protein in zebrafish larvae. A thyroid hormone-dependent GH3 cell viability assay supported the hypothesis that FLCMs act as thyroid hormone disrupting chemicals. It was also determined that FLCMs containing aliphatic ring structures may have a higher potential for T3 antagonism compared to FLCMs without an aliphatic ring. Molecular docking in silico suggested that FLCMs may affect biological functions of thyroxine binding globulin, membrane receptor integrin, and thyroid receptor beta. Lastly, the visual motor response of zebrafish in red- and green-light was significantly inhibited following exposure to FLCMs. Taken together, we demonstrate that FLCMs can act as thyroid hormone disruptors to induce visual dysfunction in zebrafish via several molecular mechanisms.

Effects of pethoxamid treatment on the disposition of thyroxine in rats

Pethoxamid (PXA) is a chloroacetamide herbicide that works by inhibiting the germination of target weeds in crops. PXA is not a genotoxic agent, however, in a two-year chronic toxicity study, incidence of thyroid follicular cell hyperplasia was observed in male rats treated at a high dose. Many non-mutagenic chemicals, including agrochemicals are known to produce thyroid hyperplasia in rodents through a hepatic metabolizing enzyme induction mode of action (MoA). In this study, the effects of oral gavage PXA treatment at 300 mg/kg for 7 days on the disposition of intravenously (iv) administered radio-labeled thyroxine ([125I]-T4) was assessed in bile-duct cannulated (BDC) rats. Another group of animals were treated with phenobarbital (PB, 100 mg/kg), a known enzyme inducer, serving as a positive control. The results showed significant increase (p < 0.01) in the mean liver weights in the PB and PXA-treated groups relative to the control group. The serum total T4 radioactivity Cmax and AUC0–4 values for PB and PXA-treated groups were lower than for the control group, suggesting increased clearance from serum. The mean percentages of administered radioactivity excreted in bile were 7.96 ± 0.38%, 16.13 ± 5.46%, and 11.99 ± 2.80% for the control, PB and PXA groups, respectively, indicating increased clearance via the bile in the treated animals. These data indicate that PXA can perturb the thyroid hormone homeostasis in rats by increasing T4 elimination in bile, possibly through enzyme induction mechanism similar to PB. In contrast to humans, the lack of high affinity thyroid binding globulin (TBG) in rats perhaps results in enhanced metabolism of T4 by uridine diphosphate glucuronosyl transferase (UGT). Since this liver enzyme induction MoA for thyroid hyperplasia by PB is known to be rodent specific, PXA effects on thyroid can also be considered not relevant to humans. The data from this study also suggest that incorporating a BDC rat model to determine thyroid hormone disposition using [125I]-T4 is valuable in a thyroid mode of action analysis.

Lactate transporter MCT1 in hepatic stellate cells promotes fibrotic collagen expression in nonalcoholic steatohepatitis.

Circulating lactate is a fuel source for liver metabolism but may exacerbate metabolic diseases such as nonalcoholic steatohepatitis (NASH). Indeed, haploinsufficiency of lactate transporter monocarboxylate transporter 1 (MCT1) in mice reportedly promotes resistance to hepatic steatosis and inflammation. Here, we used adeno-associated virus (AAV) vectors to deliver thyroxin binding globulin (TBG)-Cre or lecithin-retinol acyltransferase (Lrat)-Cre to MCT1fl/fl mice on a choline-deficient, high-fat NASH diet to deplete hepatocyte or stellate cell MCT1, respectively. Stellate cell MCT1KO (AAV-Lrat-Cre) attenuated liver type 1 collagen protein expression and caused a downward trend in trichrome staining. MCT1 depletion in cultured human LX2 stellate cells also diminished collagen 1 protein expression. Tetra-ethylenglycol-cholesterol (Chol)-conjugated siRNAs, which enter all hepatic cell types, and hepatocyte-selective tri-N-acetyl galactosamine (GN)-conjugated siRNAs were then used to evaluate MCT1 function in a genetically obese NASH mouse model. MCT1 silencing by Chol-siRNA decreased liver collagen 1 levels, while hepatocyte-selective MCT1 depletion by AAV-TBG-Cre or by GN-siRNA unexpectedly increased collagen 1 and total fibrosis without effect on triglyceride accumulation. These findings demonstrate that stellate cell lactate transporter MCT1 significantly contributes to liver fibrosis through increased collagen 1 protein expression in vitro and in vivo, while hepatocyte MCT1 appears not to be an attractive therapeutic target for NASH.

Lactate transporter MCT1 in hepatic stellate cells promotes fibrotic collagen expression in nonalcoholic steatohepatitis

Circulating lactate is a fuel source for liver metabolism but may exacerbate metabolic diseases such as nonalcoholic steatohepatitis (NASH). Indeed, haploinsufficiency of lactate transporter monocarboxylate transporter 1 (MCT1) in mice reportedly promotes resistance to hepatic steatosis and inflammation. Here, we used adeno-associated virus (AAV) vectors to deliver thyroxin binding globulin (TBG)-Cre or lecithin-retinol acyltransferase (Lrat)-Cre to MCT1fl/fl mice on a choline-deficient, high-fat NASH diet to deplete hepatocyte or stellate cell MCT1, respectively. Stellate cell MCT1KO (AAV-Lrat-Cre) attenuated liver type 1 collagen protein expression and caused a downward trend in trichrome staining. MCT1 depletion in cultured human LX2 stellate cells also diminished collagen 1 protein expression. Tetra-ethylenglycol-cholesterol (Chol)-conjugated siRNAs, which enter all hepatic cell types, and hepatocyte-selective tri-N-acetyl galactosamine (GN)-conjugated siRNAs were then used to evaluate MCT1 function in a genetically obese NASH mouse model. MCT1 silencing by Chol-siRNA decreased liver collagen 1 levels, while hepatocyte-selective MCT1 depletion by AAV-TBG-Cre or by GN-siRNA unexpectedly increased collagen 1 and total fibrosis without effect on triglyceride accumulation. These findings demonstrate that stellate cell lactate transporter MCT1 significantly contributes to liver fibrosis through increased collagen 1 protein expression in vitro and in vivo, while hepatocyte MCT1 appears not to be an attractive therapeutic target for NASH.

Hypothyroidism among Children with Nephrotic Syndrome Admitted to a Tertiary Care Centre.

Nephrotic syndrome is a glomerular disease characterized by massive urinary protein loss occurring in children. Proteinuria also leads to loss of thyroid binding globulin affecting thyroid function. This study aimed to find out the prevalence of hypothyroidism among children with nephrotic syndrome admitted to a tertiary care centre. A descriptive cross-sectional study was conducted among children with nephrotic syndrome admitted to a tertiary care centre from 06 July 2020 to 06 June 2021 after obtaining ethical approval from the Ethical Review Committee. They were tested for free T3, free T4 and TSH. A convenience sampling method was used. The point estimate was calculated at a 90% Confidence Interval. Among 69 children with nephrotic syndrome, the prevalence of hypothyroidism was 49 (71.01%) (62.03-80.00, 90% Confidence Interval). The prevalence of hypothyroidism among children with nephrotic syndrome was higher than other studies done in similar settings. children; hypothyroidism; nephrotic syndrome; prevalence.

AAV-mediated hepatic expression of SLC30A10 and the Thr95Ile variant attenuates manganese excess and other phenotypes in Slc30a10-deficient mice

The manganese (Mn) export protein SLC30A10 is essential for Mn excretion via the liver and intestines. Patients with SLC30A10 deficiency develop Mn excess, dystonia, liver disease, and polycythemia. Recent genome-wide association studies revealed a link between the SLC30A10 variant T95I and markers of liver disease. The invivo relevance of this variant has yet to be investigated. Using invitro and invivo models, we explore the impact of the T95I variant on SLC30A10 function. While SLC30A10 I95 expressed at lower levels than T95 in transfected cell lines, both T95 and I95 variants protected cells similarly from Mn-induced toxicity. Adeno-associated virus 8-mediated expression of T95 or I95 SLC30A10 using the liver-specific thyroxine binding globulin promoter normalized liver Mn levels in mice with hepatocyte Slc30a10 deficiency. Furthermore, Adeno-associated virus-mediated expression of T95 or I95 SLC30A10 normalized red blood cell parameters and body weights and attenuated Mn levels and differential gene expression in livers and brains of mice with whole body Slc30a10 deficiency. While our invivo data do not indicate that the T95I variant significantly compromises SLC30A10 function, it does reinforce the notion that the liver is a key site of SLC30A10 function. It also supports the idea that restoration of hepatic SLC30A10 expression is sufficient to attenuate phenotypes in SLC30A10 deficiency.

Exploring the mechanism of interaction between TBG and halogenated thiophenols: Insights from fluorescence analysis and molecular simulation

Thyroxine-binding globulin (TBG) plays a vital role in regulating metabolism, growth, organ differentiation, and energy homeostasis, exerting significant effects in various key metabolic pathways. Halogenated thiophenols (HTPs) exhibit high toxicity and harmfulness to organisms, and numerous studies have demonstrated their thyroid-disrupting effects. To understand the mechanism of action of HTPs on TBG, a combination of competitive binding experiments, multiple fluorescence spectroscopy techniques, molecular docking, and molecular simulations was employed to investigate the binding mechanism and identify the binding site. The competition binding assay between HTPs and ANS confirmed the competition of HTPs with thyroid hormone T4 for the active site of TBG, resulting in changes in the TBG microenvironment upon the binding of HTPs to the active site. Key amino acid residues involved in the binding process of HTPs and TBG were further investigated through residue energy decomposition. The distribution of high-energy contributing residues was determined. Analysis of root-mean-square deviation (RMSD) demonstrated the stability of the HTPs-TBG complex. These findings confirm the toxic mechanism of HTPs in thyroid disruption, providing a fundamental reference for accurately assessing the ecological risk of pollutants and human health. Providing mechanistic insights into how HTPS causes thyroid diseases.