Subclinical liver traits are associated with structural and hemodynamic brain imaging markers

Characterization of brain morphology associated with metabolic dysfunction-associated steatotic liver disease in the UK Biobank

BACKGROUND

Emerging evidence has linked metabolic dysfunction-associated steatotic liver disease (MASLD) with accelerated cognitive decline and dementia. We aimed to investigate the associations of MASLD with volumes of total brain tissue and subcortical grey matter, and white matter microstructures in the UK Biobank.

METHODS

This cross-sectional study included 29,195 individuals (aged 45-82 years) from the UK Biobank who undertook a magnetic resonance imaging (MRI) sub-study between 2014 and 2022. The brain MRI covers three modalities (T1, T2 FLAIR, and diffusion). Volumes of grey matter, subcortical grey matter structures, and regional cortex were derived from T1-weighted images. Fractional anisotropy (FA) and mean diffusivity (MD) were derived from diffusion tensor imaging (DTI) to assess global and tract-specific microstructure. MASLD was defined as the MRI-derived proton density fat fraction (MRI-PDFF) ≥5% and the presence of at least one cardiometabolic criterion. Data were analysed using multiple linear regression models.

RESULTS

MASLD was significantly associated with smaller volumes of total grey matter and subcortical grey matter (p < 0.05) and reduced Alzheimer's disease (AD)-signature cortical thickness (multivariable-adjusted β = -0.04; 95% confidence interval [CI]: -0.07, -0.01). Having MASLD was associated with higher total white matter hyperintensity (WMH) volume (multivariable-adjusted β = 0.12; 95% CI: 0.10, 0.15). For white matter microstructure, MASLD was associated with increased global FA (multivariable-adjusted β = 0.05; 95% CI: 0.03, 0.08) and reduced global MD (multivariable-adjusted β = -0.04; 95% CI: -0.07, -0.01).

CONCLUSIONS

Brain morphology associated with MASLD is characterized by smaller subcortical grey matter volume and higher coherence but lower magnitudes of white matter microstructure.

Cardiovascular disease and metabolic dysfunction-associated steatotic liver disease: pathophysiology and diagnostic aspects

Metabolic dysfunction-associated steatotic liver disease (MASLD) can be interpreted as the hepatic expression of metabolic syndrome, which is estimated to affect 30% of the adult population. Obesity, dyslipidaemia, arterial hypertension, and T2DM are considered significant risk factors of MASLD. The relationship is two-way with MASLD found in up to 75% of patients with T2DM. Importantly, MASLD is associated with increased risk of cardiovascular diseases (CVD) such as arrhythmia, atherosclerotic heart disease, heart failure, and CVD-associated mortality. In addition, MASLD patients present with a high prevalence of major adverse cardiac events, which calls for systematic surveillance of CVD in MASLD. This review focuses on the pathophysiology behind development of CVD in MASLD, the types of cardiovascular complications, morbidity and survival, and suggestions for evaluation of patients with MASLD.

Impact of non-alcoholic fatty liver disease on cognition and brain changes: a comprehensive review

This review explores the correlation of non-alcoholic fatty liver disease (NAFLD) with cognitive function and brain changes. A comprehensive search of relevant studies in the PubMed database up to June 2024 was conducted, including various study designs such as cross-sectional, longitudinal, case-control, and cohort studies. Data were extracted from 24 studies, focusing on study design, sample size, NAFLD diagnosis, control of confounders, key findings, and limitations. Neuropsychological tests utilized within each study were grouped into relevant cognitive domains. Statistical analyses and comparisons were also performed on the observed changes in brain parameters across the studies. The meta-analysis on the domain of general cognition was conducted. Results indicated that NAFLD was significantly associated with general cognition, executive function, attention, and memory. NAFLD impacts the total brain volume, the volumes of specific brain regions and certain high-intensity brain regions, the cerebral blood flow and perfusion, the integrity of nerve fiber bundles, and the brain abnormalities or lesions such as cerebral hemorrhage, cerebral microbleeds, and white matter lesions. NAFLD also affects the thickness and surface area of certain cortical regions and the resting-state brain function MRI indicators in specific brain areas. Despite these findings, the included studies varied in design, population characteristics, and outcome measures, which introduced heterogeneity that might influence the generalizability of the results. Overall, NAFLD is associated with a decline in cognitive function and alterations in certain brain parameters. Furthermore, NAFLD may exert its influence on cognition by impacting brain structure.

A narrative review about cognitive impairment in Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD): Another matter to face through a holistic approach

BACKGROUND

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most common chronic hepatic disorder worldwide in both adults and children. It is well established that MASLD represents the hepatic manifestation of the metabolic syndrome whose definition includes the presence of obesity, type 2 diabetes (T2D), dyslipidemia, hypertension and hypercoagulability. All these conditions contribute to a chronic inflammatory status which may impact on blood brain barrier (BBB) integrity leading to an impaired function of central nervous system (CNS).

AIM OF REVIEW

Since the mechanisms underlying the brain-liver-gut axis derangement are still inconclusive, the present narrative review aims to make a roundup of the most recent studies regarding the cognitive decline in MASLD also highlighting possible therapeutic strategies to reach a holistic advantage for the patients.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Due to its ever-growing prevalence, the MASLD-related mental dysfunction represents an enormous socio-economic burden since it largely impacts on the quality of life of patients as well as on their working productivity. Indeed, cognitive decline in MASLD translates in low concentration and processing speed, reduced memory, sleepiness but also anxiety and depression. Chronic systemic inflammation, hyperammonemia, genetic background and intestinal dysbiosis possibly contribute to the cognitive decline in MASLD patients. However, its diagnosis is still underestimated since the leading mechanisms are multi-faceted and unexplained and do not exist standardized diagnostic tools or cognitive test strategies. In this scenario, nutritional and lifestyle interventions as well as intestinal microbiota manipulation (probiotics, fecal transplantation) may represent new approaches to counteract mental impairment in these subjects. In sum, to face the "mental aspect" of this multifactorial disease which is almost unexplored, cognitive tools should be introduced in the management of MASLD patients.

Baseline liver fibrosis-4 score correlates to the progression of anxiety and cognitive impairment in patients with Parkinson's disease

Background

Non-alcoholic fatty liver disease (NAFLD) or liver fibrosis may share similar pathophysiological features with Parkinson's disease (PD), yet their correlation was unclear. This study aimed to explore their correlation between PD and liver fibrosis using the fibrosis-4 score (FIB-4) as a surrogate marker.

Methods

We analyzed Parkinson's Progression Markers Initiative (PPMI) data and enrolled PD patients with comprehensive baseline and 5-year follow-up time-point clinical data. Participants were categorized based on FIB-4 levels to assess the association between FIB-4 scores and various clinical scales, controlling for potential confounders. Differences in the progression of clinical scales over five years were compared using generalized linear mixed models (GLMM).

Results

Baseline FIB-4 levels positively correlated to scores of baseline section III of the Unified-Parkinson Disease Rating Scale (UPDRS III) (r = 0.145, p = 0.017), Epworth Sleepiness Scale (EPSS) (r = 0.140, P = 0.022), Hopkins Verbal Learning Test (HVLT)-delayed recall (r = 0.128, P = 0.036) and HVLT-retention (r = 0.128, p = 0.036). GLMM analysis revealed an independent correlation between FIB-4 subgroup*time and several clinical scales including the State-trait Anxiety Inventory (STAI), Symbol Digit Modalities Test (SDMT), Semantic Fluency Test (SF), HVLT-total recall, and HVLT-delayed recall, with the high FIB-4 subgroup exhibiting a greater decline in these scores compared to the low FIB-4 subgroup (all p<0.05).

Conclusion

Elevated baseline FIB-4 correlated to more severe baseline daytime sleepiness, motor symptoms, and memory function in PD patients, along with a more rapid decline in cognitive functions such as executive function, information processing ability, and memory. Additionally, a high FIB-4 might confer a protective effect against anxiety.

Metabolic dysfunction-associated steatotic liver disease is associated with effects on cerebral perfusion and white matter integrity

It is unclear whether early metabolic and inflammatory aberrations in the liver are associated with detrimental changes in brain structure and cognitive function. This cross-sectional study examines putative associations between metabolic dysfunction-associated steatotic liver disease (MASLD) and brain health in 36-55 year-old participants with obesity (n = 70) from the BARICO study (BAriatric surgery Rijnstate and Radboudumc neuroImaging and Cognition in Obesity). The participants underwent brain magnetic resonance imaging to study brain volumes and cortical thickness (3T MRI including T1-weighted magnetization-prepared rapid gradient-echo sequence), cerebral blood perfusion (arterial spin labeling) and white matter integrity (diffusion weighted imaging to assess mean-skeletonized mean diffusivity and fluid-attenuated inversion recovery to detect the presence of white matter hyperintensities (WMH)). The participants additionally performed neuropsychological tests to assess global cognition, working and episodic memory, verbal fluency and the ability to shift attention. Liver biopsies were collected and liver dysfunction was examined with histopathological, biochemical, and gene expression analyses. Linear regression analyses were performed between liver and brain parameters and the influence of body-mass index, diabetes and hypertension was explored. Early stages of liver disease were not associated with cognitive status but with cerebrovascular changes independently of age, sex, BMI, diabetes and hypertension: hepatic fibrosis development was associated with higher spatial coefficient of variation (sCoV) in the nucleus accumbens (NAcc), reflecting greater variations in cerebral perfusion and reduced vascular efficiency. Elevated hepatic levels of free cholesterol and cholesteryl esters were associated with increased WMH, indicating cerebral small vessel disease. RNA-seq and pathway analyses identified associations between sCoV in NAcc and WMH and the expression of hepatic genes involved in inflammation and cellular stress. Additionally, sCoV in NAcc correlated with plasma IL-6 levels suggesting that systemic-low grade inflammation may, at least partly, mediate this relationship. In conclusion, this study demonstrates that specific features of liver dysfunction (e.g. free cholesterol, onset of fibrosis) are associated with subtle cerebrovascular impairments, when changes in cognitive performance are not yet noticeable. These findings highlight the need for future research on therapeutic strategies that normalize metabolic-inflammatory aberrations in the liver to reduce the risk of cognitive decline.

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.

Implications of fitting a two-compartment model in single-shell diffusion MRI

It is becoming increasingly common for studies to fit single-shell diffusion MRI data to a two-compartment model, which comprises a hindered cellular compartment and a freely diffusing isotropic compartment. These studies consistently find that the fraction of the isotropic compartment (f) is sensitive to white matter (WM) conditions and pathologies, although the actual biological source of changes infhas not been validated. In this work we put aside the biological interpretation offand study the sensitivity implications of fitting single-shell data to a two-compartment model. We identify a nonlinear transformation between the one-compartment model (diffusion tensor imaging, DTI) and a two-compartment model in which the mean diffusivities of both compartments are effectively fixed. While the analytic relationship implies that fitting this two-compartment model does not offer any more information than DTI, it explains why metrics derived from a two-compartment model can exhibit enhanced sensitivity over DTI to certain types of WM processes, such as age-related WM differences. The sensitivity enhancement should not be viewed as a substitute for acquiring multi-shell data. Rather, the results of this study provide insight into the consequences of choosing a two-compartment model when only single-shell data is available.

Avenues within the gut-liver-brain axis linking chronic liver disease and symptoms

Symptoms of fatigue, social withdrawal and mood disturbances are commonly encountered in patients with chronic liver disease and have a detrimental effect on patient quality of life. Treatment options for these symptoms are limited and a current area of unmet medical need. In this review, we will evaluate the potential mechanistic avenues within the gut-liver-brain axis that may be altered in the setting of chronic liver disease that drive the development of these symptoms. Both clinical and pre-clinical studies will be highlighted as we discuss how perturbations in host immune response, microbiome, neural responses, and metabolites composition can affect the central nervous system.