Hepatic Unsaturated Fatty Acids Are Linked to Lower Degree of Fibrosis in Non-alcoholic Fatty Liver Disease

Ketogenesis supports hepatic polyunsaturated fatty acid homeostasis via fatty acid elongation

Ketogenesis is a dynamic metabolic conduit supporting hepatic fat oxidation particularly when carbohydrates are in short supply. Ketone bodies may be recycled into anabolic substrates, but a physiological role for this process has not been identified. Here, we use mass spectrometry-based 13C-isotope tracing and shotgun lipidomics to establish a link between hepatic ketogenesis and lipid anabolism. Unexpectedly, mouse liver and primary hepatocytes consumed ketone bodies to support fatty acid biosynthesis via both de novo lipogenesis (DNL) and polyunsaturated fatty acid (PUFA) elongation. While an acetoacetate intermediate was not absolutely required for ketone bodies to source DNL, PUFA elongation required activation of acetoacetate by cytosolic acetoacetyl-coenzyme A synthetase (AACS). Moreover, AACS deficiency diminished free and esterified PUFAs in hepatocytes, while ketogenic insufficiency depleted PUFAs and increased liver triacylglycerols. These findings suggest that hepatic ketogenesis influences PUFA metabolism, representing a molecular mechanism through which ketone bodies could influence systemic physiology and chronic diseases.

Associations between dietary fatty acid and plasma fatty acid composition in non-alcoholic fatty liver disease: secondary analysis from a randomised trial with a hypoenergetic low-carbohydrate high-fat and intermittent fasting diet

Dietary fatty acids (FA) affect metabolic risk factors. The aim of this study was to explore if changes in dietary fat intake during energy restriction were associated with plasma FA composition. The study also investigated if these changes were associated with changes in liver fat, liver stiffness and plasma lipids among persons with non-alcoholic fatty liver disease. Dietary and plasma FA were investigated in patients with non-alcoholic fatty liver disease (n 48) previously enrolled in a 12-week-long open-label randomised controlled trial comparing two energy-restricted diets: a low-carbohydrate high-fat diet and intermittent fasting diet (5:2), to a control group. Self-reported 3 d food diaries were used for FA intake, and plasma FA composition was analysed using GC. Liver fat content and stiffness were measured by MRI and transient elastography. Changes in intake of total FA (r 0·41; P = 0·005), SFA (r 0·38; P = 0·011) and MUFA (r 0·42; P = 0·004) were associated with changes in liver stiffness. Changes in plasma SFA (r 0·32; P = 0·032) and C16 : 1n-7 (r 0·33; P = 0·028) were positively associated with changes in liver fat, while total n-6 PUFA (r -0·33; P = 0·028) and C20 : 4n-6 (r -0·42; P = 0·005) were inversely associated. Changes in dietary SFA, MUFA, cholesterol and C20:4 were positively associated with plasma total cholesterol and LDL-cholesterol. Modifying the composition of dietary fats during dietary interventions causes changes in the plasma FA profile in patients with non-alcoholic fatty liver disease. These changes are associated with changes in liver fat, stiffness, plasma cholesterol and TAG. Replacing SFA with PUFA may improve metabolic parameters in non-alcoholic fatty liver disease patients during weight loss treatment.

Greater hepatic lipid saturation is associated with impaired glycaemic regulation in men with metabolic dysfunction-associated steatotic liver disease but is not altered by 6 weeks of exercise training

AIMS

To examine the impact of impaired glycaemic regulation (IGR) and exercise training on hepatic lipid composition in men with metabolic dysfunction-associated steatotic liver disease (MASLD).

MATERIALS AND METHODS

In Part A (cross-sectional design), 40 men with MASLD (liver proton density fat fraction [PDFF] ≥5.56%) were recruited to one of two groups: (1) normal glycaemic regulation (NGR) group (glycated haemoglobin [HbA1c] < 42 mmol∙mol-1 [<6.0%]; n = 14) or (2) IGR group (HbA1c ≥ 42 mmol∙mol-1 [≥6.0%]; n = 26). In Part B (randomized controlled trial design), participants in the IGR group were randomized to one of two 6-week interventions: (1) exercise training (EX; 70%-75% maximum heart rate; four sessions/week; n = 13) or (2) non-exercise control (CON; n = 13). Saturated (SI; primary outcome), unsaturated (UI) and polyunsaturated (PUI) hepatic lipid indices were determined using proton magnetic resonance spectroscopy. Additional secondary outcomes included liver PDFF, HbA1c, fasting plasma glucose (FPG), homeostatic model assessment of insulin resistance (HOMA-IR), peak oxygen uptake (VO2 peak), and plasma cytokeratin-18 (CK18) M65, among others.

RESULTS

In Part A, hepatic SI was higher and hepatic UI was lower in the IGR versus the NGR group (p = 0.038), and this hepatic lipid profile was associated with higher HbA1c levels, FPG levels, HOMA-IR and plasma CK18 M65 levels (rs ≥0.320). In Part B, hepatic lipid composition and liver PDFF were unchanged after EX versus CON (p ≥ 0.257), while FPG was reduced and VO2 peak was increased (p ≤ 0.030). ΔVO2 peak was inversely associated with Δhepatic SI (r = -0.433) and positively associated with Δhepatic UI and Δhepatic PUI (r ≥ 0.433).

CONCLUSIONS

Impaired glycaemic regulation in MASLD is characterized by greater hepatic lipid saturation; however, this composition is not altered by 6 weeks of moderate-intensity exercise training.

Ketogenesis supports hepatic polyunsaturated fatty acid homeostasis via fatty acid elongation

Therapeutic interventions targeting hepatic lipid metabolism in metabolic dysfunction-associated steatotic liver disease (MASLD) and steatohepatitis (MASH) remain elusive. Using mass spectrometry-based stable isotope tracing and shotgun lipidomics, we established a novel link between ketogenesis and MASLD pathophysiology. Our findings show that mouse liver and primary hepatocytes consume ketone bodies to support fatty acid (FA) biosynthesis via both de novo lipogenesis (DNL) and FA elongation. Analysis of 13 C-labeled FAs in hepatocytes lacking mitochondrial D-β-hydroxybutyrate dehydrogenase (BDH1) revealed a partial reliance on mitochondrial conversion of D-βOHB to acetoacetate (AcAc) for cytoplasmic DNL contribution, whereas FA elongation from ketone bodies was fully dependent on cytosolic acetoacetyl-CoA synthetase (AACS). Ketone bodies were essential for polyunsaturated FA (PUFA) homeostasis in hepatocytes, as loss of AACS diminished both free and esterified PUFAs. Ketogenic insufficiency depleted liver PUFAs and increased triacylglycerols, mimicking human MASLD, suggesting that ketogenesis supports PUFA homeostasis, and may mitigate MASLD-MASH progression in humans.

This Is What Metabolic Dysfunction-Associated Steatotic Liver Disease Looks Like: Potential of a Multiparametric MRI Protocol

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a prevalent condition with a broad spectrum defined by liver biopsy. This gold standard method evaluates three features: steatosis, activity (ballooning and lobular inflammation), and fibrosis, attributing them to certain grades or stages using a semiquantitative scoring system. However, liver biopsy is subject to numerous restrictions, creating an unmet need for a reliable and reproducible method for MASLD assessment, grading, and staging. Noninvasive imaging modalities, such as magnetic resonance imaging (MRI), offer the potential to assess quantitative liver parameters. This review aims to provide an overview of the available MRI techniques for the three criteria evaluated individually by liver histology. Here, we discuss the possibility of combining multiple MRI parameters to replace liver biopsy with a holistic, multiparametric MRI protocol. In conclusion, the development and implementation of such an approach could significantly improve the diagnosis and management of MASLD, reducing the need for invasive procedures and paving the way for more personalized treatment strategies.

Lipid Metabolism in Metabolic-Associated Steatotic Liver Disease (MASLD)

Metabolic-associated steatotic liver disease (MASLD) is a cluster of pathological conditions primarily developed due to the accumulation of ectopic fat in the hepatocytes. During the severe form of the disease, i.e., metabolic-associated steatohepatitis (MASH), accumulated lipids promote lipotoxicity, resulting in cellular inflammation, oxidative stress, and hepatocellular ballooning. If left untreated, the advanced form of the disease progresses to fibrosis of the tissue, resulting in irreversible hepatic cirrhosis or the development of hepatocellular carcinoma. Although numerous mechanisms have been identified as significant contributors to the development and advancement of MASLD, altered lipid metabolism continues to stand out as a major factor contributing to the disease. This paper briefly discusses the dysregulation in lipid metabolism during various stages of MASLD.

Multi-omic network analysis identified betacellulin as a novel target of omega-3 fatty acid attenuation of western diet-induced nonalcoholic steatohepatitis

Clinical and preclinical studies established that supplementing diets with ω3 polyunsaturated fatty acids (PUFA) can reduce hepatic dysfunction in nonalcoholic steatohepatitis (NASH) but molecular underpinnings of this action were elusive. Herein, we used multi-omic network analysis that unveiled critical molecular pathways involved in ω3 PUFA effects in a preclinical mouse model of western diet induced NASH. Since NASH is a precursor of liver cancer, we also performed meta-analysis of human liver cancer transcriptomes that uncovered betacellulin as a key EGFR-binding protein upregulated in liver cancer and downregulated by ω3 PUFAs in animals and humans with NASH. We then confirmed that betacellulin acts by promoting proliferation of quiescent hepatic stellate cells, inducing transforming growth factor-β2 and increasing collagen production. When used in combination with TLR2/4 agonists, betacellulin upregulated integrins in macrophages thereby potentiating inflammation and fibrosis. Taken together, our results suggest that suppression of betacellulin is one of the key mechanisms associated with anti-inflammatory and anti-fibrotic effects of ω3 PUFA on NASH.

Dietary Long-Chain Fatty Acids Accelerate Metabolic Dysfunction in Guinea Pigs with Non-Alcoholic Steatohepatitis

The composition of dietary fatty acids may be important for the development and progression of metabolic syndrome and non-alcoholic steatohepatitis (NASH). This study investigated the effect of two high-fat diets based on coconut oil, containing predominantly medium-chain fatty acids (MCFA), or cocoa butter, containing mainly long-chain fatty acids (LCFA), on glucose homeostasis and NASH in guinea pigs following 16 and 32 weeks of diet. At week 16, glucose intolerance was increased in the LCFA animals compared to the MCFA animals (p < 0.001), with both groups differing from the controls by week 32 (p < 0.0001), supported by increased hemoglobin A1c (p < 0.05). NASH was present in both high-fat groups from week 16, with advancing fibrosis appearing more progressive in the LCFA animals at week 16. In agreement, gene expression showed overall increased expression of NASH target genes in the LCFA animals compared to the MCFA animals at weeks 16 and 32 (p < 0.05 and p < 0.0001, respectively). The LCFA animals also displayed increased plasma uric acid at both time points (p < 0.05), a phenomenon linked to NASH in humans. In conclusion, this study reports that a diet high in LCFA promotes metabolic imbalance and may accelerate NASH-associated hepatic fibrosis. This highlights the importance of a critical evaluation of fatty acid composition when investigating NASH-associated endpoints.

Hepatic and serum branched-chain fatty acid profile in patients with nonalcoholic fatty liver disease: A case-control study

OBJECTIVE

Alterations in the hepatic lipidome are a crucial factor involved in the pathophysiology of nonalcoholic fatty liver disease (NAFLD). The aim of this study was to evaluate the serum and hepatic profile of branched-chain fatty acids (BCFAs) in patients with different stages of NAFLD.

METHODS

This was a case-control study performed in 27 patients without NAFLD, 49 patients with nonalcoholic fatty liver, and 17 patients with nonalcoholic steatohepatitis, defined by liver biopsies. Serum and hepatic levels of BCFAs were analyzed by gas chromatography-mass spectrometry. The hepatic expression of genes involved in the endogenous synthesis of BCFAs was analyzed by real-time quantitative polymerase chain reaction (RT-qPCR).

RESULTS

A significant increase in hepatic BCFAs was found in subjects with NAFLD compared with those without NAFLD; no differences were observed in serum BCFAs between study groups. Trimethyl BCFAs, iso-BCFAs, and anteiso-BCFAs were increased in subjects with NAFLD (either nonalcoholic fatty liver or nonalcoholic steatohepatitis) compared with those without NAFLD. Correlation analysis showed a relationship between hepatic BCFAs and the histopathological diagnosis of NAFLD, as well as other histological and biochemical parameters related to this disease. Gene expression analysis in liver showed that the mRNA levels of BCAT1, BCAT2, and BCKDHA were upregulated in patients with NAFLD.

CONCLUSIONS

These results suggest that the increased production of liver BCFAs might be related to NAFLD development and progression.

Maternal Western diet is associated with distinct preclinical pediatric NAFLD phenotypes in juvenile nonhuman primate offspring

Pediatric NAFLD has distinct and variable pathology, yet causation remains unclear. We have shown that maternal Western-style diet (mWSD) compared with maternal chow diet (CD) consumption in nonhuman primates produces hepatic injury and steatosis in fetal offspring. Here, we define the role of mWSD and postweaning Western-style diet (pwWSD) exposures on molecular mechanisms linked to NAFLD development in a cohort of 3-year-old juvenile nonhuman primates offspring exposed to maternal CD or mWSD followed by CD or Western-style diet after weaning. We used histologic, transcriptomic, and metabolomic analyses to identify hepatic pathways regulating NAFLD. Offspring exposed to mWSD showed increased hepatic periportal collagen deposition but unchanged hepatic triglyceride levels and body weight. mWSD was associated with a downregulation of gene expression pathways underlying HNF4α activity and protein, and downregulation of antioxidant signaling, mitochondrial biogenesis, and PPAR signaling pathways. In offspring exposed to both mWSD and pwWSD, liver RNA profiles showed upregulation of pathways promoting fibrosis and endoplasmic reticulum stress and increased BiP protein expression with pwWSD. pwWSD increased acylcarnitines and decreased anti-inflammatory fatty acids, which was more pronounced when coupled with mWSD exposure. Further, mWSD shifted liver metabolites towards decreased purine catabolism in favor of synthesis, suggesting a mitochondrial DNA repair response. Our findings demonstrate that 3-year-old offspring exposed to mWSD but weaned to a CD have periportal collagen deposition, with transcriptional and metabolic pathways underlying hepatic oxidative stress, compromised mitochondrial lipid sensing, and decreased antioxidant response. Exposure to pwWSD worsens these phenotypes, triggers endoplasmic reticulum stress, and increases fibrosis. Overall, mWSD exposure is associated with altered expression of candidate genes and metabolites related to NAFLD that persist in juvenile offspring preceding clinical presentation of NAFLD.

Graduate Student Literature Review: A scoping review on the impact of consumption of dairy products on phosphatidylcholine and lysophosphatidylcholine in circulation and the liver in human studies and animal models

Dairy consumption is inversely related to the risk of developing type 2 diabetes in epidemiological research. One proposed hypothesis is that phospholipid (PL) species associated with dairy consumption mediate this relationship. This scoping review aimed to identify the existing literature in animal and human trials investigating the impact of dairy products, including milk, yogurt, and cheese as well as dairy-derived PL supplementation on PL and its species in the circulation, summarizing the characteristics of these studies and identifying research gaps. A systematic search was conducted across 3 databases (PubMed, Scopus, and Web of Science) in March 2021. Of 2,427 identified references, 15 studies (7 humans and 8 animal studies) met the eligibility criteria and were included in the final narrative synthesis. The evidence base was heterogeneous, involving a variety of clinical and preclinical studies, metabolically healthy or obese/diabetic participants or animal models, and displayed mixed findings. Circulating postprandial concentrations of total PL were elevated acutely but unchanged after longer intervention with dairy products. The PL concentration remained stable even after a high dosage of milk supplemented with dairy-derived PL, which may be related to increased fecal excretion; however, certain phosphatidylcholine (PC) or lysophosphatidylcholine species were increased in circulation by interventions. These include several PC species with 32 to 38 total carbons in addition to the dairy biomarkers C15:0 and C17:0. The results of this scoping review demonstrate a small body of literature indicating that dairy products can influence blood concentrations of PC and lysophosphatidylcholine species in both rodents and humans without alteration of total PL and PC. There is a lack of well-designed trials in humans and animals that explore the potential differences between individual dairy foods on PL species. In addition, trials to understand the bioactive properties of PC and lysophosphatidylcholine species on cardiometabolic risk are needed.

Human centenarian-associated SIRT6 mutants modulate hepatocyte metabolism and collagen deposition in multilineage hepatic 3D spheroids

Non-alcoholic fatty liver disease (NAFLD), encompassing fatty liver and its progression into nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and hepatocellular carcinoma (HCC), is one of the rapidly rising health concerns worldwide. SIRT6 is an essential nuclear sirtuin that regulates numerous pathological processes including insulin resistance and inflammation, and recently it has been implicated in the amelioration of NAFLD progression. SIRT6 overexpression protects from formation of fibrotic lesions. However, the underlying molecular mechanisms are not fully delineated. Moreover, new allelic variants of SIRT6 (N308K/A313S) were recently associated with the longevity in Ashkenazi Jews by improving genome maintenance and DNA repair, suppressing transposons and killing cancer cells. Whether these new SIRT6 variants play different or enhanced roles in liver diseases is currently unknown. In this study, we aimed to clarify how these new centenarian-associated SIRT6 genetic variants affect liver metabolism and associated diseases. We present evidence that overexpression of centenarian-associated SIRT6 variants dramatically altered the metabolomic and secretomic profiles of unchallenged immortalized human hepatocytes (IHH). Most amino acids were increased in the SIRT6 N308K/A313S overexpressing IHH when compared to IHH transfected with the SIRT6 wild-type sequence. Several unsaturated fatty acids and glycerophospholipids were increased, and ceramide tended to be decreased upon SIRT6 N308K/A313S overexpression. Furthermore, we found that overexpression of SIRT6 N308K/A313S in a 3D hepatic spheroid model formed by the co-culture of human immortalized hepatocytes (IHH) and hepatic stellate cells (LX2) inhibited collagen deposition and fibrotic gene expression in absence of metabolic or dietary challenges. Hence, our findings suggest that novel longevity associated SIRT6 N308K/A313S variants could favor the prevention of NASH by altering hepatocyte proteome and lipidome.

Plasma Fatty Acid Composition Is Associated with Histological Findings of Nonalcoholic Steatohepatitis

The relationship between advanced nonalcoholic steatohepatitis (NASH) and plasma fatty acid composition remains unknown. We aimed to examine the plasma fatty acid composition in biopsy-confirmed nonalcoholic fatty liver disease (NAFLD) and evaluate the relationship between histological findings and fatty acid composition. Overall, 235 patients (134 women) with NAFLD were enrolled. Comprehensive blood chemistry tests and histological examinations of liver samples were conducted. Multivariate analyses adjusted for age, sex, body mass index, alanine aminotransferase, hemoglobin A1c, creatinine, total cholesterol, triglyceride, and NAFLD Activity Score values showed that lower levels of arachidic, behenic, α-linolenic, eicosatetraenoic, docosapentaenoic, and docosahexaenoic acids and higher levels of mead acid were associated with fibrosis stage 3–4. Furthermore, higher lauric acid, myristic acid, and palmitic acid levels and monounsaturated fatty acids such as palmitoleic acid and oleic acid were significantly associated with high NAS in analyses adjusted for the same factors and fibrosis stage. The plasma fatty acid composition was associated with the histological evidence of NASH. Increased synthesis of fatty acids is associated with NASH; insufficient intake of n-3 essential fatty acids and reduced elongation of fatty acids are associated with fibrosis in NASH. These features may help clinicians to understand and treat advanced NASH cases.