Glycogen storage disease type 1a (GSD Ia) is an inborn error of metabolism caused by mutations in the G6PC gene, encoding the catalytic subunit of glucose-6-phosphatase. Early symptoms include severe fasting intolerance, failure to thrive and hepatomegaly, biochemically associated with nonketotic hypoglycemia, fasting hyperlactidemia, hyperuricemia and hyperlipidemia. Dietary management is the cornerstone of treatment aiming at maintaining euglycemia, prevention of secondary metabolic perturbations and long-term complications, including liver (hepatocellular adenomas and carcinomas), kidney and bone disease (hypovitaminosis D and osteoporosis). As impaired vitamin A homeostasis also associates with similar symptoms and is coordinated by the liver, we here analysed whether vitamin A metabolism is affected in GSD Ia patients and liver-specific G6pc^−/− knock-out mice. Serum levels of retinol and retinol binding protein 4 (RBP4) were significantly increased in both GSD Ia patients and L-G6pc^−/− mice. In contrast, hepatic retinol levels were significantly reduced in L-G6pc^−/− mice, while hepatic retinyl palmitate (vitamin A storage form) and RBP4 levels were not altered. Transcript and protein analyses indicate an enhanced production of retinol and reduced conversion the retinoic acids (unchanged LRAT, Pnpla2/ATGL and Pnpla3 up, Cyp26a1 down) in L-G6pc^−/− mice. Aberrant expression of genes involved in vitamin A metabolism was associated with reduced basal messenger RNA levels of markers of inflammation (Cd68, Tnfα, Nos2, Il-6) and fibrosis (Col1a1, Acta2, Tgfβ, Timp1) in livers of L-G6pc^−/− mice. In conclusion, GSD Ia is associated with elevated serum retinol and RBP4 levels, which may contribute to disease symptoms, including osteoporosis and hepatic steatosis.

The plasma metabolome reflects the physiological state of various biological processes and can serve as a proxy for disease risk. Plasma metabolite variation, influenced by genetic and epigenetic mechanisms, can also affect the cellular microenvironment and blood cell epigenetics. The interplay between the plasma metabolome and the blood cell epigenome remains elusive. In this study, we performed an epigenome-wide association study (EWAS) of 1183 plasma metabolites in 693 participants from the LifeLines-DEEP cohort and investigated the causal relationships in DNA methylation–metabolite associations using bidirectional Mendelian randomization and mediation analysis. After rigorously adjusting for potential confounders, including genetics, we identified five robust associations between two plasma metabolites (l-serine and glycine) and three CpG sites located in two independent genomic regions (cg14476101 and cg16246545 in PHGDH and cg02711608 in SLC1A5) at a false discovery rate of less than 0.05. Further analysis revealed a complex bidirectional relationship between plasma glycine/serine levels and DNA methylation. Moreover, we observed a strong mediating role of DNA methylation in the effect of glycine/serine on the expression of their metabolism/transport genes, with the proportion of the mediated effect ranging from 11.8 to 54.3%. This result was also replicated in an independent population-based cohort, the Rotterdam Study. To validate our findings, we conducted in vitro cell studies which confirmed the mediating role of DNA methylation in the regulation of PHGDH gene expression. Our findings reveal a potential feedback mechanism in which glycine and serine regulate gene expression through DNA methylation.

Background/Objectives: Nutraceuticals, including short-chain fatty acids (SCFAs) and antioxidants (AOXs), are nutrient-derived bioactive compounds considered as potential treatments for metabolic-associated steatotic liver disease (MASLD). However, in vitro studies of their effects are limited by inconsistent experimental conditions, including differences in cell lines, methods of steatosis induction, and culture media, and by reliance on qualitative rather than quantitative assessments. Here, we systematically evaluate the anti-steatotic potential of eight commonly used nutraceuticals—three SCFAs (butyrate, acetate, and propionate) and five AOXs (resveratrol, curcumin, berberine, chlorogenic acid, and vitamin E)—using a standardized in vitro approach. Methods: Following a systematic literature review to identify common experimental conditions, we developed an assay to validate steatosis induction and quantified the effects of the nutraceuticals. For our studies we used the HepG2 liver cancer cell line and the Fa2N-4 immortalized hepatocyte cell line. Steatosis was modeled by stimulating cells with free fatty acids and fructose for 48 h. Nutraceuticals were added either concurrently with steatotic stimulation, to assess preventive effects, or after 24 h to assess therapeutic effects. Anti-steatotic drugs (resmetirom, semaglutide, obeticholic acid, and a DGAT2 inhibitor) were included as positive controls. Intracellular triglyceride levels were measured to quantify steatosis. Results: A systematic review of 46 studies revealed large differences in culture conditions, steatosis induction, and nutraceutical assessment. In our experiments, most nutraceuticals did not reduce intracellular triglycerides, with the exception of vitamin E. Surprisingly, butyrate, berberine, and curcumin increased triglyceride accumulation. Resmetirom was the only drug that significantly decreased triglycerides, while obeticholic acid, semaglutide, and the DGAT2 inhibitor showed minimal or inconsistent effects. Fa2N-4 cells were generally more sensitive than HepG2 cells, showing larger absolute changes in triglyceride levels in response to both nutraceuticals and resmetirom. Conclusions: We established a standardized in vitro assay to evaluate the anti-steatotic potential of nutraceuticals. Using this system, we found that SCFAs and AOXs did not consistently reduce intracellular triglycerides, highlighting the need for quantitative assessments and careful validation when studying anti-steatotic interventions in vitro.

Human liver organoids (HLOs) and liver-on-a-chip (LoC) systems are emerging as physiologically relevant human models for studying liver function, disease, and drug metabolism, often in combination with human induced pluripotent stem cell (hiPSC)-derived tissues. However, hiPSC-derived models often display batch-to-batch variation and incomplete maturation, and the contribution of microfluidic flow to hepatic maturation remains insufficiently characterized. Here, we developed a cryopreservable and scalable workflow to generate hiPSC-derived hepatic organoids that can be directly matured to either static HLOs or LoC systems, enabling matched comparison of both platforms. Transcriptomic and functional characterization revealed progressive hepatic maturation during organoid differentiation, including increased expression of liver-specific metabolic pathways, enhanced albumin secretion, and increased CYP3A4 activity. Compared to mature HLOs, LoCs exposed to continuous microfluidic flow exhibited transcriptomic profiles suggesting further maturation, with increased enrichment of pathways related to lipid metabolism, xenobiotic metabolism, transport, and tissue organization. These findings demonstrate that microfluidic perfusion promotes hepatic metabolic specialization compared to static organoid culture while maintaining donor-specific characteristics. Together, this study establishes a robust hiPSC-derived LoC platform and highlights the potential of flow-based systems for improved modeling of human liver physiology, disease mechanisms, and drug responses.