Non-alcoholic fatty liver disease to metabolic dysfunction-associated fatty liver disease: Conceptual changes for clinicians, researchers and patients

Utility of Human Relevant Preclinical Animal Models in Navigating NAFLD to MAFLD Paradigm

Fatty liver disease is an emerging contributor to disease burden worldwide. The past decades of work established the heterogeneous nature of non-alcoholic fatty liver disease (NAFLD) etiology and systemic contributions to the pathogenesis of the disease. This called for the proposal of a redefinition in 2020 to that of metabolic dysfunction-associated fatty liver disease (MAFLD) to better reflect the current understanding of the disease. To date, several clinical cohort studies comparing NAFLD and MAFLD hint at the relevancy of the new nomenclature in enriching for patients with more severe hepatic injury and extrahepatic comorbidities. However, the underlying systemic pathogenesis is still not fully understood. Preclinical animal models have been imperative in elucidating key biological mechanisms in various contexts, including intrahepatic disease progression, interorgan crosstalk and systemic dysregulation. Furthermore, they are integral in developing novel therapeutics against MAFLD. However, substantial contextual variabilities exist across different models due to the lack of standardization in several aspects. As such, it is crucial to understand the strengths and weaknesses of existing models to better align them to the human condition. In this review, we consolidate the implications arising from the change in nomenclature and summarize MAFLD pathogenesis. Subsequently, we provide an updated evaluation of existing MAFLD preclinical models in alignment with the new definitions and perspectives to improve their translational relevance.

Obesity is an important determinant of severity in newly defined metabolic dysfunction-associated fatty liver disease

BACKGROUND

The recently proposed definition of metabolic dysfunction-associated fatty liver disease (MAFLD) is based on the co-existence of hepatic steatosis with other metabolic disorders, including obesity and metabolic risk abnormalities such as hyperglycemia, high blood pressure and dyslipidemia. This study aimed to assess MAFLD severity according to the presence of metabolic abnormalities and obesity.

METHODS

Using transient elastography, hepatic steatosis and fibrosis severity were assessed by measuring the controlled attenuation parameter and liver stiffness measurement. A total of 1163 patients with MAFLD were categorized into the following four groups according to metabolic risk abnormalities and obesity presence: non-obese without metabolic risk abnormality group (Group 1; reference group); non-obese with metabolic risk abnormality group (Group 2); obese without metabolic risk abnormality group (Group 3); and obese with metabolic risk abnormality group (Group 4). A multiple logistic regression analysis was performed to determine severe hepatic steatosis and fibrosis risk in each group in both unadjusted and adjusted models.

RESULTS

In the adjusted model, the odds ratios (ORs) [95% confidence interval (CI)] for severe hepatic steatosis in Groups 2, 3, and 4 were 1.07 (0.61-1.88), 2.43 (1.44-4.08), and 4.07 (2.56-6.48), respectively (P_trend < 0.001). For liver fibrosis, compared with Group 1, Group 2 showed no significant increases in OR, whereas Groups 3 and 4 (obese groups) showed significant increases (OR = 4.70, 95% CI: 1.24-17.82 and OR = 6.43, 95% CI: 1.88-22.02, respectively).

CONCLUSIONS

Obesity, rather than metabolic abnormality, is the principal determinant of severe hepatic steatosis and fibrosis in patients with MAFLD.

Prevalence and characteristics of MAFLD in Chinese adults aged 40 years or older: A community-based study

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) was recently proposed to be renamed metabolic dysfunction-associated fatty liver disease (MAFLD) with the diagnostic criteria revised. We investigated the similarities and differences in the prevalence and clinical characteristics of MAFLD and NAFLD in Chinese adults.

METHODS

A cross-sectional study of 9980 Chinese individuals aged 40 years or older was performed between 2011 and 2012 using randomized, stratified cluster sampling in Shanghai, China. A detailed questionnaire and the results of abdominal ultrasonography, a standardized 2-h 75-g oral glucose tolerance test and blood biochemical examinations were collected.

RESULTS

A total of 9927 subjects were included in this study. The prevalence of MAFLD (40.3%) was significantly higher than that of NAFLD (36.9%) (P < 0.05). MAFLD was highly prevalent in type 2 diabetes mellitus (T2DM) (53.8%), impaired fasting glucose (35.7%) and impaired glucose tolerance (40.9%). High risk of advanced fibrosis based on fibrosis-4 was highly prevalent (14.7%) in lean MAFLD with T2DM. Among 9927 subjects, 3481 (35.1%) fulfilled the diagnostic criteria for MAFLD and NAFLD (MAFLD+NAFLD+), 521 (5.2%) MAFLD+NAFLD-, and 181 (1.8%) MAFLD-NAFLD+. The MAFLD+NAFLD- group had more significant metabolic disorders than those in the MAFLD+NAFLD+ group (all P < 0.05). Among MAFLD-NAFLD+ subjects, 82.9% had metabolic disorders.

CONCLUSIONS

The new definition of MAFLD may better reflect the pathogenesis related to metabolism. Future research should focus on studying the natural history, pathogenesis and treatment effectivity of the overlap and non-overlap of NAFLD and MAFLD subjects.