The association between thyroid hormones and MAFLD is mediated by obesity and metabolic disorders and varies among MAFLD subtypes

Examining the Pathogenesis of MAFLD and the Medicinal Properties of Natural Products from a Metabolic Perspective

Metabolic-associated fatty liver disease (MAFLD), characterized primarily by hepatic steatosis, has become the most prevalent liver disease worldwide, affecting approximately two-fifths of the global population. The pathogenesis of MAFLD is extremely complex, and to date, there are no approved therapeutic drugs for clinical use. Considerable evidence indicates that various metabolic disorders play a pivotal role in the progression of MAFLD, including lipids, carbohydrates, amino acids, and micronutrients. In recent years, the medicinal properties of natural products have attracted widespread attention, and numerous studies have reported their efficacy in ameliorating metabolic disorders and subsequently alleviating MAFLD. This review aims to summarize the metabolic-associated pathological mechanisms of MAFLD, as well as the natural products that regulate metabolic pathways to alleviate MAFLD.

MAFLD as part of systemic metabolic dysregulation

Nonalcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases worldwide. In recent years, a new terminology and definition of metabolic dysfunction-associated fatty liver disease (MAFLD) has been proposed. Compared to the NAFLD definition, MAFLD better emphasizes the pathogenic role of metabolic dysfunction in the development and progression of this highly prevalent condition. Metabolic disorders, including overweight/obesity, type 2 diabetes mellitus (T2DM), atherogenic dyslipidemia and hypertension, are often associated with systemic organ dysfunctions, thereby suggesting that multiple organ damage can occur in MAFLD. Substantial epidemiological evidence indicates that MAFLD is not only associated with an increased risk of liver-related complications, but also increases the risk of developing several extra-hepatic diseases, including new-onset T2DM, adverse cardiovascular and renal outcomes, and some common endocrine diseases. We have summarized the current literature on the adverse effect of MAFLD on the development of multiple extrahepatic (cardiometabolic and endocrine) complications and examined the role of different metabolic pathways and organ systems in the progression of MAFLD, thus providing new insights into the role of MAFLD as a multisystem metabolic disorder. Our narrative review aimed to provide insights into potential mechanisms underlying the known associations between MAFLD and extrahepatic diseases, as part of MAFLD as a multisystem disease, in order to help focus areas for future drug development targeting not only liver disease but also the risk of extrahepatic complications.

Metabolic Dysfunction-Associated Fatty Liver Disease (MAFLD) and Thyroid Function in Childhood Obesity: A Vicious Circle?

Metabolic dysfunction-associated fatty liver disease (MAFLD) is a multisystem disorder characterized by the presence of fatty liver degeneration associated with excess adiposity or prediabetes/type 2 diabetes or metabolic dysregulation. An intricate relationship between the liver and thyroid has been reported in both health and disease. Simultaneously, there is a strong correlation between obesity and both MAFLD and thyroid dysfunction. In this narrative review, we highlighted the relationship between MAFLD and thyroid function in children and adolescents with obesity in order to explore how thyroid hormones (THs) act as predisposing factors in the onset, progression, and sustainability of MAFLD. THs are integral to the intricate balance of metabolic activities, ensuring energy homeostasis, and are indispensable for growth and development. Regarding liver homeostasis, THs have been suggested to interact with liver lipid homeostasis through a series of processes, including stimulating the entry of free fatty acids into the liver for esterification into triglycerides and increasing mitochondrial β-oxidation of fatty acids to impact hepatic lipid accumulation. The literature supports a correlation between MAFLD and obesity, THs and obesity, and MAFLD and THs; however, results in the pediatric population are very limited. Even though the underlying pathogenic mechanism involved in the relationship between MAFLD and thyroid function remains not fully elucidated, the role of THs as predisposing factors of MAFLD could be postulated. A potential vicious circle among these three conditions cannot be excluded. Identifying novel elements that may contribute to MAFLD could offer a practical approach to assessing children at risk of developing the condition.

Association between low-normal thyroid function and advanced liver fibrosis in metabolic dysfunction-associated fatty liver disease patients: a retrospective cohort study

Background

Recent studies have found that thyroid function may be associated with the occurrence and development of advanced liver fibrosis in patients with metabolic dysfunction-associated fatty liver disease (MAFLD). However, the majority of such research has consisted of cross-sectional studies. This retrospective cohort study aimed to investigate the effect of low-normal thyroid function on advanced liver fibrosis in MAFLD patients over a 5-year period.

Methods

This retrospective cohort study enrolled 825 outpatients and inpatients with MAFLD who attended the Third Affiliated Hospital of Sun Yat-sen University (Guangzhou, China) between January 2011 and December 2018. Based on plasma thyroid hormone and thyroid-stimulating hormone levels, these patients were divided into two groups, namely a low-normal thyroid function group and a strict-normal thyroid function group. The fibrosis-4 score was used to assess advanced liver fibrosis. A chi-square test was conducted to compare the occurrence of advanced fibrosis between the groups.

Results

Among the 825 MAFLD patients, 117 and 708 were defined as having low-normal thyroid function and strict-normal thyroid function, respectively. Follow-up data were available for 767 patients (93.0%) during a 5-year period. Eight (7.5%) MAFLD patients with low-normal thyroid function and 26 (3.9%) with strict-normal thyroid function developed advanced liver fibrosis and the cumulative incidence was not significantly different (P = 0.163). Stratification analysis showed that the lean MAFLD patients (body mass index ≤ 23 kg/m2) with low-normal thyroid function had a higher risk of advanced liver fibrosis than the lean MAFLD patients with strict-normal thyroid function (P < 0.05).

Conclusion

Low-normal thyroid function is associated with advanced liver fibrosis among lean MAFLD patients.

Low-Normal Thyroid Function Is Not Associated with Either Non-Alcoholic Fatty Liver Disease or with Metabolic Dysfunction-Associated Fatty Liver Disease

BACKGROUND

The association of low-normal thyroid function (LNTF) with non-alcoholic fatty liver disease (NAFLD) or metabolic dysfunction-associated fatty liver disease (MAFLD) is controversial; thus, the aim of this study is to determine this association.

METHODS

NAFLD was evaluated by controlled attenuation parameter of transient elastography. Patients were classified by MAFLD criteria. LNTF was defined as TSH levels of 2.5 to 4.5 mIU/L and were divided into three different cut-off points (>4.5 to 5.0, >3.1, and >2.5 mIU/L). Associations between LNTF, NAFLD, and MAFLD were evaluated by univariate and multivariate logistic regression analyses.

RESULTS

A total of 3697 patients were included; 59% (n = 2179) were male, and median age and body mass index were 48 (43-55) years and 25.9 (23.6-28.5) kg/m², respectively, and 44% (n = 1632) were diagnosed with NAFLD. THS levels of 2.5 and 3.1 showed significant associations with the presence of NAFLD and MAFLD; however, LNTF did not show an independent association with the presence of NAFLD or MAFLD in multivariate analysis. According to different cut-off points, patients with LNTF presented similar risks for NAFLD as the general population.

CONCLUSION

LNTF is not associated with NAFLD or MAFLD. Patients with high LNTF are equally at risk for NAFLD as the general population.