Thyroid function and non-alcoholic fatty liver disease in hyperthyroidism patients

Hepatic thyroid hormone receptor-β signalling: Mechanisms and recent advancements in the treatment of metabolic dysfunction-associated steatohepatitis

The pharmacotherapy of metabolic dysfunction-associated steatotic liver disease (MASLD) and its progressive form, the metabolic dysfunction-associated steatohepatitis (MASH), remains a hot topic in research and a largely unmet need in clinical practice. As the first approval of a disease-specific drug, resmetirom, was regarded as a milestone for the management of this common liver disease, this comprehensive and updated review aimed to highlight the importance of the hepatic thyroid hormone (TH) receptor (THR)-β signalling for the treatment of MASH, with a special focus on resmetirom. First, the genomic and non-genomic actions of the liver-directed THR-β mediated mechanisms are summarized. THR-β has a key role in hepatic lipid and carbohydrate metabolism; disruption of THR-β signalling leads to dysmetabolism, thus promoting MASLD and possibly its progression to MASH and cirrhosis. In the clinical setting, this is translated into a significant association between primary hypothyroidism and MASLD, as confirmed by recent meta-analyses. An association between MASLD and subclinical intrahepatic hypothyroidism (i.e. a state of relatively low hepatic triiodothyronine concentrations, with circulating TH concentrations within the normal range) is also emerging and under investigation. In line with this, the favourable results of the phase 3 placebo-controlled MAESTRO trials led to the recent conditional approval of resmetirom by the US FDA for treating adults with MASH and moderate-to-advanced fibrosis. This conditional approval of resmetirom opened a new window to the management of this common and burdensome liver disease, thus bringing the global scientific community in front of new perspectives and challenges.

Association of free triiodothyronine and total triiodothyronine with nonalcoholic fatty liver disease: from National Health and Nutrition Examination Survey and Mendelian randomization study

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is associated with multiple factors, yet the relationship between NAFLD and thyroid-related biomarkers remains unclear. This study aims to elucidate this potential linkage.

METHODS

Utilizing data from the US National Health and Nutrition Examination Survey (NHANES), we explored the possible associations between thyroid-related biomarkers and NAFLD through multivariable logistic regression, subgroup analysis, and interaction tests. A bidirectional Mendelian randomization (MR) approach complemented by various sensitivity analyses was then employed to ascertain these relationships' causality.

RESULTS

Our NHANES analysis indicated significant associations between elevated levels of free triiodothyronine (FT3) [odds ratio (OR): 2.59, 95% confidence interval (CI): 1.50-4.49] and total triiodothyronine (TT3) (OR: 2.01, 95% CI: 1.27-3.18) with the prevalence of NAFLD. MR findings reinforced the causal relationship, demonstrating that NAFLD may elevate FT3 (β: 0.05, 95% CI: 0.01-0.09) and TT3 (β: 0.08, 95% CI: 0.02-0.14) levels. Additionally, thyroid-stimulating hormone (TSH) was confirmed as an independent risk factor for NAFLD (OR: 1.10, 95% CI: 1.04-1.18), with specific MR sensitivity analyses supporting the robustness of these results.

CONCLUSION

This study indicates potential elevations in FT3, TT3, and thyroglobulin levels associated with NAFLD, while also identifying TSH as a risk factor for NAFLD. These findings underscore the importance of routine thyroid function monitoring both in the general population and particularly in individuals with NAFLD.

Thyromimetics and MASLD: Unveiling the Novel Molecules Beyond Resmetirom

BACKGROUND

Resmetirom, the first FDA-approved drug for nonalcoholic steatohepatitis (NASH) with fibrosis in obese patients, when combined with lifestyle modifications, improves NASH resolution and reduces fibrosis by at least one stage. Low thyroid hormone (T3) levels are linked to a higher risk of developing metabolic dysfunction-associated steatotic liver disease (MASLD). Epidemiological studies have confirmed the positive correlation between hypothyroidism and MASLD. Unraveling the molecular mechanisms of T3 signaling pathways in MASLD will enhance the prospects of identifying effective and specific targets. Therefore, this review discusses the significant role of thyroid hormones in the homeostasis of fat metabolism and describes the possible molecular mechanisms of thyromimetics in the treatment of MASLD.

METHODS

A comprehensive search in PubMed and EMBASE was conducted using the keywords "thyromimetics and liver diseases," "thyroid hormone and liver diseases," "hypothyroidism and liver diseases," "T3, T4 and liver disease," and "resmetirom and liver disease." Relevant papers published before October 2024 were included.

RESULTS

T3 treatment enhances mitochondrial respiration, biogenesis, β-oxidation, and mitophagy, reducing liver lipid accumulation. However, T3 treatment causes cardiotoxicity through thyroid hormone receptor (THR)α agonistic activity. To address this, molecules with high THRβ agonistic but lower THRα activity have been developed. Besides resmetirom, other THRβ agonists like TG68, CS27109, MB07811, and KB-141 show promising results in experimental studies. These molecules upregulate THRβ target genes, activate genes for fatty acid β-oxidation in mitochondria and fatty acid breakdown in peroxisomes, downregulate the genes involved in de novo lipogenesis, reduce inflammation by downregulating NF-κB/JNK/STAT3 signaling pathways, and accelerate fibrosis resolution by downregulating the expressions of fibrosis marker genes in NASH liver tissue.

CONCLUSION

Future clinical studies should thoroughly investigate THRβ agonists, including TG68, CS27109, MB07811, and KB-141.

Correlation Between Thyroid Hormone and Controlled Attenuation Parameters: A Cross-Sectional Population-Based Study

Objective

The aim of the present study was to investigate how thyroid hormone levels are related to controlled attenuation parameters (CAP), which may provide insights for understanding the role of these factors in hepatic steatosis.

Methods

A total of 3461 participants who underwent CAP diagnosis between 2018 and 2023 were included. The associations between thyroid hormone levels and CAP were evaluated through multiple linear regression, restricted cubic splines (RCS) and threshold effect analyses.

Results

Multiple linear regression analysis revealed an inverse relationship between free thyroxine (FT4) and CAP, with a coefficient of -0.855 and a confidence interval of -1.297 to -0.412. The negative connection in a subset examination persisted in males [-0.729 (-1.295, -0.162)] and females [-1.234 (-1.996, -0.473)]. A strong correlation was found between free 3,5,3'-triiodothyronine (FT3) and CAP, with values of 2.182 (1.154, 3.211). Further analysis was conducted on both male [1.626 (0.188, 3.065)] and female [2.835 (1.137, 4.533)] subgroups. In the severe liver steatosis group, there was a significant negative correlation between FT3 and CAP based on the subgroup analysis stratified by the level of liver steatosis [-3.804 (-6.711, -0.898)]. The RCS analysis showed a nonlinear association between FT4 and CAP, with a turning point at 11.14 pmol/L.

Conclusion

There was a significant linear and nonlinear relationship between FT4, FT3 and CAP. Thyroid hormones could have a significant impact on liver steatosis, offering fresh perspectives on how to prevent and treat this condition.

Causal validation of the relationship between 35 blood and urine biomarkers and hyperthyroidism: a bidirectional Mendelian randomization study and meta-analysis

Background

Hyperthyroidism is an endocrine disorder with a relatively low global prevalence but significantly higher incidence among females compared to males. The onset age primarily ranges from 30 to 50, although it is not limited to this age group. Challenges in the treatment of hyperthyroidism include individualized treatment plan formulation, management of side effects, and prediction of disease progression, necessitating comprehensive consideration to achieve more effective therapy and management. Mendelian randomization studies can reveal more precise therapeutic targets between blood and urine biomarkers and hyperthyroidism, providing more decadent treatment options for the condition.

Methods

The study will build upon the omics Mendelian randomization (MR) framework by conducting MR analysis using 35 blood and urine biomarkers separately for two distinct databases of hyperthyroidism. Subsequently, the results will undergo meta-analysis and multiple corrections to ensure accuracy and reliability. Finally, positive findings will undergo reverse MR validation to verify causal relationships with hyperthyroidism.

Results

In the British database, the MR analysis of Total bilirubin levels about hyperthyroidism yielded an odds ratio (OR) of 1.097 (95% CI: 0.951-1.265, P = 0.205). Conversely, in the Thyroid Omics Association database, the MR analysis revealed an OR of 1.283 (95% CI: 1.122-1.467, P = 0.0002) for the same relationship. Meta-analysis of the MR analysis results from both databases, following multiple corrections, resulted in an OR of 1.192 (95% CI: 1.081-1.314, P = 0.015). Additionally, the direction of beta values in the MR analysis results from both databases was consistent.

Conclusion

The urine biomarker total bilirubin levels may contribute to an increased risk of hyperthyroidism and accelerate its progression, thus representing a risk factor for the condition.

Endocrine aspects of metabolic dysfunction-associated steatotic liver disease (MASLD): Beyond insulin resistance

While the association of metabolic dysfunction-associated steatotic liver disease (MASLD) with obesity and insulin resistance is widely appreciated, there are a host of complex interactions between the liver and other endocrine axes. While it can be difficult to definitively distinguish direct causal relationships and those attributable to increased adipocyte mass, there is substantial evidence of the direct and indirect effects of endocrine dysregulation on the severity of MASLD, with strong evidence that low levels of growth hormone, sex hormones, and thyroid hormone promote the development and progression of disease. The impact of steroid hormones, e.g. cortisol and dehydroepiandrosterone, and adipokines is much more divergent. Thoughtful assessment, based on individual risk factors and findings, and management of non-insulin endocrine axes is essential in the evaluation and management of MASLD. Multiple therapeutic options have emerged that leverage various endocrine axes to reduce the fibroinflammatory cascade in MASH.

Understanding the Relationship between Nonalcoholic Fatty Liver Disease and Thyroid Disease

The prevalence of hypothyroidism in patients with nonalcoholic fatty liver disease (NAFLD) is high (22.4%). Thyroid hormones (THs) regulate many metabolic activities in the liver by promoting the export and oxidation of lipids, as well as de novo lipogenesis. They also control hepatic insulin sensitivity and suppress hepatic gluconeogenesis. Because of its importance in lipid and carbohydrate metabolism, the involvement of thyroid dysfunction in the pathogenesis of NAFLD seems plausible. The mechanisms implicated in this relationship include high thyroid-stimulating hormone (TSH) levels, low TH levels, and chronic inflammation. The activity of the TH receptor (THR)-β in response to THs is essential in the pathogenesis of hypothyroidism-induced NAFLD. Therefore, an orally active selective liver THR-β agonist, Resmetirom (MGL-3196), was developed, and has been shown to reduce liver fat content, and as a secondary end point, to improve nonalcoholic steatohepatitis. The treatment of NAFLD with THR-β agonists seems quite promising, and other agonists are currently under development and investigation. This review aims to shine a light on the pathophysiological and epidemiological evidence regarding this relationship and the effect that treatment with THs and selective liver THR-β agonists have on hepatic lipid metabolism.

The nonlinear relationship between thyroid function parameters and metabolic dysfunction-associated fatty liver disease

BACKGROUND

The relationship between thyroid function parameters and metabolic dysfunction-associated fatty liver disease (MAFLD) remains controversial. Additionally, little is known about the relationship between thyroid function parameters and MAFLD in the Chinese population.

METHODS

We conducted a retrospective cross-sectional study involving 177,540 individuals with thyroid function tests and MAFLD diagnosis from 2010-2018. The association between thyroid function parameters and MAFLD was evaluated on a continuous scale with restricted cubic spline (RCS) models and by the prior-defined centile categories with multivariable-adjusted logistic regression models. Thyroid function parameters included free triiodothyronine (FT3), free tetra-iodothyronine (FT4), and thyroid stimulating hormone (TSH). Additionally, fully adjusted RCS models stratified by sex, age, and location were studied.

RESULTS

In the RCS models, the risk of MAFLD increased with higher levels of FT3 when FT3 <5.58pmol/L, while the risk of MAFLD decreased with higher levels of FT3 when FT3 ≥5.58pmol/L (P nonlinearity <0.05). While RCS analysis suggested that the FT4 levels had a negative association with MAFLD (P nonlinearity <0.05), indicating an increase in FT4 levels was associated with a decreased risk of MAFLD. RCS analysis suggested an overall positive association between the concentration of TSH and MAFLD risk (P nonlinearity <0.05). The rising slope was sharper when the TSH concentration was less than 1.79uIU/mL, which indicated the association between TSH and MAFLD risk was tightly interrelated within this range. The multivariable logistic regression showed that populations in the 81st-95th centile had the highest risk of MAFLD among all centiles of FT3/TSH, with the 1st-5th centile as the reference category.

CONCLUSIONS

Our study suggested nonlinear relationships between thyroid function parameters and MAFLD. Thyroid function parameters could be additional modifiable risk factors apart from the proven risk factors to steer new avenues regarding MAFLD prevention and treatment.

Metabolic Signatures of Youth Exposure to Mixtures of Per- and Polyfluoroalkyl Substances: A Multi-Cohort Study

BACKGROUND

Exposure to per- and polyfluoroalkyl substances (PFAS) is ubiquitous and has been associated with an increased risk of several cardiometabolic diseases. However, the metabolic pathways linking PFAS exposure and human disease are unclear.

OBJECTIVE

We examined associations of PFAS mixtures with alterations in metabolic pathways in independent cohorts of adolescents and young adults.

METHODS

Three hundred twelve overweight/obese adolescents from the Study of Latino Adolescents at Risk (SOLAR) and 137 young adults from the Southern California Children's Health Study (CHS) were included in the analysis. Plasma PFAS and the metabolome were determined using liquid-chromatography/high-resolution mass spectrometry. A metabolome-wide association study was performed on log-transformed metabolites using Bayesian regression with a g-prior specification and g-computation for modeling exposure mixtures to estimate the impact of exposure to a mixture of six ubiquitous PFAS (PFOS, PFHxS, PFHpS, PFOA, PFNA, and PFDA). Pathway enrichment analysis was performed using Mummichog and Gene Set Enrichment Analysis. Significance across cohorts was determined using weighted Z -tests.

RESULTS

In the SOLAR and CHS cohorts, PFAS exposure was associated with alterations in tyrosine metabolism (meta-analysis p = 0.00002 ) and de novo fatty acid biosynthesis (p = 0.03 ), among others. For example, when increasing all PFAS in the mixture from low (∼ 30 th percentile) to high (∼ 70 th percentile), thyroxine (T4), a thyroid hormone related to tyrosine metabolism, increased by 0.72 standard deviations (SDs; equivalent to a standardized mean difference) in the SOLAR cohort (95% Bayesian credible interval (BCI): 0.00, 1.20) and 1.60 SD in the CHS cohort (95% BCI: 0.39, 2.80). Similarly, when going from low to high PFAS exposure, arachidonic acid increased by 0.81 SD in the SOLAR cohort (95% BCI: 0.37, 1.30) and 0.67 SD in the CHS cohort (95% BCI: 0.00, 1.50). In general, no individual PFAS appeared to drive the observed associations.

DISCUSSION

Exposure to PFAS is associated with alterations in amino acid metabolism and lipid metabolism in adolescents and young adults. https://doi.org/10.1289/EHP11372.

Sensitivity to thyroid hormones is associated with advanced fibrosis in euthyroid patients with non-alcoholic fatty liver disease: A cross-sectional study

BACKGROUND AND AIMS

The relationship between thyroid hormone sensitivity and the occurrence of advanced hepatic fibrosis in non-alcoholic fatty liver disease (NAFLD) remains unclear. We aimed to explore the association between sensitivity to thyroid hormones and advanced fibrosis (F3-F4) of NAFLD in patients with biopsy-proven euthyroid NAFLD.

METHODS

In this study, 129 participants with biopsy-proven euthyroid NAFLD were enrolled, all of whom underwent thyroid function tests and liver biopsy. Indicators reflecting the sensitivity to thyroid hormones were also calculated. A logistic regression model was used to evaluate the association between thyroid hormone sensitivity and risk of advanced liver fibrosis.

RESULTS

Among the 129 participants, 40 (31.0%) had advanced fibrosis. Advanced fibrosis was independently associated with TSH, FT3, FT3/FT4, thyrotroph T4 resistance index (TT4RI), TSH index (TSHI), and thyroid feedback quantile-based index (TFQI) (P<0.05), even after adjusting for sex, age, and metabolic factors. The combination of TFQI with age, waist circumference (WC), triglycerides (TGs), and low-density lipoprotein cholesterol (LDL-C) performed best for advanced fibrosis diagnosis.

CONCLUSION

In euthyroid NAFLD patients, higher FT3/FT4, TFQI, TT4RI, and TSHI values were strongly associated with an increased incidence of advanced liver fibrosis. The combination of TFQI with age, WC, TGs, and LDL-C can be used as a predictor for advanced fibrosis in patients with NAFLD.

Influence of Altered Thyroid Hormone Mechanisms in the Progression of Metabolic Dysfunction Associated with Fatty Liver Disease (MAFLD): A Systematic Review

We performed a systematic review of the mechanisms of thyroid hormones (THs) associated with metabolic dysfunction associated with fatty liver disease (MAFLD). This systematic review was registered under PROSPERO (CRD42022323766). We searched the MEDLINE (via PubMed) and Embase databases from their inception to March 2022. We included studies that assessed thyroid function by measuring the serum level of THs and those involved in MAFLD. We excluded reviews, case reports, editorials, letters, duplicate studies and designed controls. Forty-three studies included MAFLD, eleven analyzed THs, and thirty-two evaluated the mechanisms of THs in MAFLD. Thyroid hormones are essential for healthy growth, development and tissue maintenance. In the liver, THs directly influence the regulation of lipid and carbohydrate metabolism, restoring the homeostatic state of the body. The selected studies showed an association of reduced levels of THs with the development and progression of MAFLD. In parallel, reduced levels of T3 have a negative impact on the activation of co-regulators in the liver, reducing the transcription of genes important in hepatic metabolism. Overall, this is the first review that systematically synthesizes studies focused on the mechanism of THs in the development and progression of MAFLD. The data generated in this systematic review strengthen knowledge of the impact of TH changes on the liver and direct new studies focusing on therapies that use these mechanisms.

Effects of Thyroid Hormones on Lipid Metabolism Pathologies in Non-Alcoholic Fatty Liver Disease

The typical modern lifestyle contributes to the development of many metabolic-related disorders, as exemplified by metabolic syndrome. How to prevent, resolve, or avoid subsequent deterioration of metabolic disturbances and the development of more serious diseases has become an important and much-discussed health issue. Thus, the question of the physiological and pathological roles of thyroid hormones (THs) in metabolism has never gone out of fashion. Although THs influence almost all organs, the liver is one of the most important targets as well as the hub of metabolic homeostasis. When this homeostasis is out of balance, diseases may result. In the current review, we summarize the common features and actions of THs, first focusing on their effects on lipid metabolism in the liver. In the second half of the review, we turn to a consideration of non-alcoholic fatty liver disease (NAFLD), a disease characterized by excessive accumulation of fat in the liver that is independent of heavy alcohol consumption. NAFLD is a growing health problem that currently affects ~25% of the world’s population. Unfortunately, there are currently no approved therapies specific for NAFLD, which, if left uncontrolled, may progress to more serious diseases, such as cirrhosis or liver cancer. This absence of effective treatment can also result in the development of non-alcoholic steatohepatitis (NASH), an aggressive form of NAFLD that is the leading cause of liver transplantation in the United States. Because THs play a clear role in hepatic fat metabolism, their potential application in the prevention and treatment of NAFLD has attracted considerable research attention. Studies that have investigated the use of TH-related compounds in the management of NAFLD are also summarized in the latter part of this review. An important take-home point of this review is that a comprehensive understanding of the physiological and pathological roles of THs in liver fat metabolism is possible, despite the complexities of this regulatory axis—an understanding that has clinical value for the specific management of NAFLD.

Sensitivity to Thyroid Hormone Indices Are Closely Associated With NAFLD

BACKGROUND

Previous studies on the association between thyroid function and non-alcoholic fatty liver disease (NAFLD) have contradicted. Acquired resistance to thyroid hormone theory might provide a reasonable explanation for these contradictions. We aimed to analyze the association between sensitivity to thyroid hormone indices with NAFLD.

METHODS

A total of 4,610 individuals from the health medical center of the First Hospital of China Medical University were included in this study. The previously used thyroid feedback quantile-based index (TFQI_FT4) was calculated. Also, we substituted free triiodothyronine (FT₃) into the TFQI formulas to get the TFQI_FT3 index. NAFLD was defined using abdominal ultrasound.

RESULTS

Study results showed that FT₃/FT₄ and TFQI_FT3 were positively correlated with the triglyceride (TG), total cholesterol (TC), and low-density lipoprotein cholesterol (LDL-C) levels (P<0.05) and negatively correlated with high-density lipoprotein cholesterol (HDL-C) level (P<0.05). In contrast, TFQI_FT4 was positively correlated with HDL-C level (P < 0.05). After adjustment for multiple confounders, FT₃, FT₃/FT₄, and TFQI_FT3 were positively associated with the risks of dyslipidemia and NAFLD (P < 0.05). TFQI_FT3 and FT₃/FT₄ performed better than TFQI_FT4 on ROC analyses for NAFLD prediction, although the diagnostic sensitivity and specificity at the optimal cut-points were low. However, no association was observed between TFQI_FT4 with the risks of dyslipidemia and NAFLD.

CONCLUSION

TFQI_FT3 and FT₃/FT₄ can be used as new indicators for predicting dyslipidemia and NAFLD, although with low sensitivity and specificity at the optimal cut-points, while TFQI_FT4 has insufficient evidence in predicting dyslipidemia and NAFLD.