Gut microbiota plays a key role in obesity and non-alcoholic fatty liver disease (NAFLD), so synbiotics could be a therapeutic alternative. We aim to evaluate a nutritional intervention together with the administration of the bacteria Akkermansia muciniphila and the antioxidant quercetin in an in vivo model of early obesity and NAFLD. 21-day-old rats were fed with control or high-fat diet for six weeks. Then, all animals received control diet supplemented with/without quercetin and/or A. muciniphila for three weeks. Gut microbiota, NAFLD-related parameters, circulating bile acids (BAs) and liver gene expression were analyzed. The colonization with A. muciniphila was associated with less body fat, while synbiotic treatment caused a steatosis remission, linked to hepatic lipogenesis modulation. The synbiotic promoted higher abundance of Cyanobacteria and Oscillospira, and lower levels of Actinobacteria, Lactococcus, Lactobacillus and Roseburia. Moreover, it favored elevated unconjugated hydrophilic BAs plasma levels and enhanced hepatic expression of BA synthesis and transport genes. A. muciniphila correlated with circulating BAs and liver lipid and BA metabolism genes, suggesting a role of this bacterium in BA signaling. Beneficial effects of A. muciniphila and quercetin combination are driven by gut microbiota modulation, the shift in BAs and the gut-liver bile flow enhancement.

Background and Aims: Recent studies suggest that mitochondrial dysfunction promotes progression to NASH by aggravating the gut‐liver status. However, the underlying mechanism remains unclear. Herein, we hypothesized that enhanced mitochondrial activity might reshape a specific microbiota signature that, when transferred to germ‐free (GF) mice, could delay NASH progression. Approach and Results: Wild‐type and methylation‐controlled J protein knockout (MCJ‐KO) mice were fed for 6 weeks with either control or a choline‐deficient, L‐amino acid–defined, high‐fat diet (CDA‐HFD). One mouse of each group acted as a donor of cecal microbiota to GF mice, who also underwent the CDA‐HFD model for 3 weeks. Hepatic injury, intestinal barrier, gut microbiome, and the associated fecal metabolome were then studied. Following 6 weeks of CDA‐HFD, the absence of methylation‐controlled J protein, an inhibitor of mitochondrial complex I activity, reduced hepatic injury and improved gut‐liver axis in an aggressive NASH dietary model. This effect was transferred to GF mice through cecal microbiota transplantation. We suggest that the specific microbiota profile of MCJ‐KO, characterized by an increase in the fecal relative abundance of Dorea and Oscillospira genera and a reduction in AF12, Allboaculum, and [Ruminococcus], exerted protective actions through enhancing short‐chain fatty acids, nicotinamide adenine dinucleotide (NAD⁺) metabolism, and sirtuin activity, subsequently increasing fatty acid oxidation in GF mice. Importantly, we identified Dorea genus as one of the main modulators of this microbiota‐dependent protective phenotype. Conclusions: Overall, we provide evidence for the relevance of mitochondria–microbiota interplay during NASH and that targeting it could be a valuable therapeutic approach.

Gut microbiota (GM) is involved in the maintenance of physiological homeostasis, thus the alteration of its composition and functionality has been associated with many pathologies such as metabolic diseases, and could also be linked with the progressive degenerative process in aging. Nowadays, life expectancy is continuously rising, so the number of elder people and the consequent related pathologies demand new strategies to achieve healthy aging. Besides, actual lifestyle patterns make metabolic diseases a global epidemic with increasing trends, responsible for a large mortality and morbidity in adulthood and also compromising the health status of later stages of life. Metabolic diseases and aging share a profile of low-grade inflammation and innate immunity activation, which may have disturbances of GM composition as the leading mechanism. Thus, GM emerges as a therapeutic target with a double impact in the elderly, counteracting both aging itself and the frequent metabolic diseases in this population. This review summarizes the role and compositional changes of the GM in aging and its modulation through nutritional interventions and physical exercise as a strategy to counteract the aging process and the related metabolic diseases.

Several hepatic disorders are influenced by gut microbiota, but its role in idiosyncratic drug-induced liver injury (iDILI), whose main causative agent is amoxicillin–clavulanate, remains unknown. This pioneering study aims to unravel particular patterns of gut microbiota composition and associated metabolites in iDILI and iDILI patients by amoxicillin–clavulanate (iDILI-AC). Thus, serum and fecal samples from 46 patients were divided into three study groups: healthy controls (n = 10), non-iDILI acute hepatitis (n = 12) and iDILI patients (n = 24). To evaluate the amoxicillin–clavulanate effect, iDILI patients were separated into two subgroups: iDILI non-caused by amoxicillin–clavulanate (iDILI-nonAC) (n = 18) and iDILI-AC patients (n = 6). Gut microbiota composition and fecal metabolome plus serum and fecal bile acid (BA) analyses were performed, along with correlation analyses. iDILI patients presented a particular microbiome profile associated with reduced fecal secondary BAs and fecal metabolites linked to lower inflammation, such as dodecanedioic acid and pyridoxamine. Moreover, certain taxa like Barnesiella, Clostridia UCG-014 and Eubacterium spp. correlated with significant metabolites and BAs. Additionally, comparisons between iDILI-nonAC and iDILI-AC groups unraveled unique features associated with iDILI when caused by amoxicillin–clavulanate. In conclusion, specific gut microbiota profiles in iDILI and iDILI-AC patients were associated with particular metabolic and BA status, which could affect disease onset and progression.

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most common cause of chronic liver disease worldwide. Fibrosis is the main prognostic factor and the last reversible stage before cirrhosis, yet therapeutic options remain limited. Given the strong contribution of gut dysbiosis to MASLD progression, strategies targeting the gut microbiota are of growing interest. This study aims to evaluate the effect of melatonin, a well-known antioxidant, anti-inflammatory and antifibrotic compound, and Akkermansia muciniphila, a next-generation probiotic, on an MASLD-associated liver fibrosis model. Eight-week-old C57BL/6J mice were fed a control or Western diet supplemented with fructose and intraperitoneal CCl₄ to induce liver fibrosis. After eight weeks, the animals received either no intervention, melatonin, A. muciniphila, or both for four weeks. Serum biochemistry, liver histology and gut and liver gene expression were evaluated and multi-omic analyses were performed, including gut microbiota profiling and faecal metabolomics. Statistical analyses assessed intergroup differences and correlations across datasets. Both interventions partially restored gut microbiota composition and functionality and modulated hepatic and intestinal gene expression. Melatonin and A. muciniphila exerted protective effects against MASLD-associated fibrosis, which supports their potential as adjunctive therapeutic strategies to mitigate liver injury through modulation of the gut–liver axis.

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most common cause of chronic liver disease worldwide. Fibrosis is the main prognostic factor and the last reversible stage before cirrhosis, yet therapeutic options remain limited. Given the strong contribution of gut dysbiosis to MASLD progression, strategies targeting the gut microbiota are of growing interest. This study aims to evaluate the effect of melatonin, a well-known antioxidant, anti-inflammatory and antifibrotic compound, and Akkermansia muciniphila, a next-generation probiotic, on a MASLD-associated liver fibrosis model. Eight-week-old C57BL/6J mice were fed with control or Western diet supplemented with fructose and intraperitoneal CCl₄ to induce liver fibrosis. After eight weeks, animals received either no intervention, melatonin, A. muciniphila, or both for four weeks. Serum biochemistry, liver histology and gut and liver gene expression were evaluated and multi-omic analyses were performed, including gut microbiota profiling and faecal metabolomics. Statistical analyses assessed intergroup differences and correlations across datasets. Both interventions partially restored gut microbiota composition and functionality and modulated hepatic and intestinal gene expression. Melatonin and A. muciniphila exerted protective effects against MASLD-associated fibrosis, which supports their potential as adjunctive therapeutic strategies to mitigate liver injury through modulation of the gut–liver axis.