Carmelo García-Monzón

Obstructive sleep apnea (OSA), characterized by intermittent hypoxia (IH), is strongly associated with metabolic syndrome and metabolic dysfunction-associated steatotic liver disease (MASLD). IH exacerbates MASLD progression through oxidative stress, inflammation, and lipid accumulation. This study aims to investigate the impact of oxygen normalization on metabolic dysfunction in OSA patients using continuous positive airway pressure (CPAP) therapy, and in mice exposed to IH followed by a reoxygenation period. In the clinical study, 76 participants (44 OSA patients and 32 controls) were analyzed. OSA patients had higher insulin resistance, triglycerides, very low density lipoprotein (VLDL) content, and liver enzyme levels, along with a higher prevalence of liver steatosis. After 18 months of CPAP therapy, OSA patients showed significant improvements in insulin resistance, lipid profiles (total cholesterol and VLDL), liver function markers (AST and albumin), and steatosis risk scores (Fatty Liver Index and OWLiver test). In the experimental study, IH induced hepatic lipid accumulation, oxidative stress, and inflammation, and reoxygenation reversed these deleterious effects in mice. At the molecular level, IH downregulated fatty acid oxidation (FAO)-related genes, thus impairing the FAO process. Reoxygenation maintained elevated levels of lipogenic genes but restored FAO gene expression and activity, suggesting enhanced lipid clearance despite ongoing lipogenesis. Indeed, serum β hydroxybutyrate, a key marker of hepatic FAO in patients, was impaired in OSA patients but normalized after CPAP therapy, supporting improved FAO function. CPAP therapy improves lipid profiles, liver function, and MASLD progression in OSA patients. Experimental findings highlight the therapeutic potential of oxygen normalization in reversing IH-induced liver damage by FAO pathway restoration, indicating a metabolic reprogramming in the liver.

Aim: To determine the prevalence of skeletal muscle alterations (SMA) in patients with meta-bolic dysfunction-associated steatotic liver disease (MASLD) and to assess the significance of circulating myokines as potential biomarkers of SMA in patients with MASLD. Material and methods: Measurements of both skeletal muscle strength and skeletal muscle mass parameters, anthropometric and metabolic features as well as serum levels of different myokines were per-formed in a cohort of 62 MASLD patients and then compared according to the stage of liver fi-brosis and hepatosteatosis degree both diagnosed by transitional elastography. Results: No sig-nificant differences were found in skeletal muscle strength and skeletal muscle mass in MASLD patients stratified according to the stage of liver fibrosis. Noteworthy, serum levels of FGF21 were significantly higher in MASLD patients with advanced hepatic fibrosis (F3-F4) than in those with lower stages of hepatic fibrosis (F0-F2) (197.49±198.27 pg/ml vs 95.62±83.67 pg/ml, p=0.049, respectively). MASLD patients with severe hepatosteatosis (S3) had significantly higher serum levels of irisin (1116.87±1161.86 pg/ml) than those with lower grades (S1-S2) (385.21±375.98 pg/ml, p=0.001). Conclusion: SMA were uncommon in our MASLD patients, particularly in those with lower stages of liver fibrosis. An increase in serum FGF21 was detected in patients with a higher stage of fibrosis with possible therapeutic implications in MASLD.

Background and Aims: Cyclooxygenase‐2 (COX‐2) is involved in different liver diseases, but little is known about the significance of COX‐2 in cholestatic injury. This study was designed to elucidate the role of COX‐2 expression in hepatocytes during the pathogenesis of obstructive cholestasis.Methods: We used genetically modified mice constitutively expressing human COX‐2 in hepatocytes. Transgenic mice (hCOX‐2‐Tg) and their wild‐type (Wt) littermates were either subjected to a mid‐abdominal laparotomy or common bile duct ligation (BDL) for 2 or 5 days. Then, we explored the mechanisms underlying the role of COX‐2 and its derived prostaglandins in liver function, and the synthesis and excretion of bile acids (BA) in response to cholestatic liver injury.Results: After BDL, hCOX‐2‐Tg mice showed lower grades of hepatic necrosis and inflammation than Wt mice, in part by a reduced hepatic neutrophil recruitment associated with lower mRNA levels of pro‐inflammatory cytokines. Furthermore, hCOX‐2‐Tg mice displayed a differential metabolic pattern of BA synthesis that led to an improved clearance after BDL‐induced accumulation. In addition, an enhanced response to the BDL‐induced oxidative stress and hepatic apoptosis was observed. In vitro experiments using hepatic cells that stably express hCOX‐2 confirmed the cytoprotective role of prostaglandin E₂ against BA toxicity.Conclusions: Taken together, our data indicate that constitutive expression of COX‐2 in hepatocytes ameliorates cholestatic liver injury in mice by reducing inflammation and cell damage and by modulating BA metabolism, pointing to a role for COX‐2 as a defensive response against cholestasis‐derived BA accumulation and injury.

Background and Aims: The molecular mechanisms driving non‐alcoholic fatty liver disease (NAFLD) are poorly understood; however, microRNAs might play a key role in these processes. We hypothesize that let‐7d‐5p could contribute to the pathophysiology of NAFLD and serve as a potential diagnostic biomarker.Methods: We evaluated let‐7d‐5p levels and its targets in liver biopsies from a cross‐sectional study including patients with NAFLD and healthy donors, and from a mouse model of NAFLD. Moreover, the induction of let‐7d‐5p expression by fatty acids was evaluated in vitro. Further, we overexpressed let‐7d‐5p in vitro to corroborate the results observed in vivo. Circulating let‐7d‐5p and its potential as a NAFLD biomarker was determined in isolated extracellular vesicles from human plasma by RT‐qPCR.Results: Our results demonstrate that hepatic let‐7d‐5p was significantly up‐regulated in patients with steatosis, and this increase correlated with obesity and a decreased expression of AKT serine/threonine kinase (AKT), insulin‐like growth factor 1 (IGF1), IGF‐I receptor (IGF1R) and insulin receptor (INSR). These alterations were corroborated in a NAFLD mouse model. In vitro, fatty acids increased let‐7d‐5p expression, and its overexpression decreased AKT, IGF‐IR and IR protein expression. Furthermore, let‐7d‐5p hindered AKT phosphorylation in vitro after insulin stimulation. Finally, circulating let‐7d‐5p significantly decreased in steatosis patients and receiver operating characteristic (ROC) analyses confirmed its utility as a diagnostic biomarker.Conclusions: Our results highlight the emerging role of let‐7d‐5p as a potential therapeutic target for NAFLD since its overexpression impairs hepatic insulin signalling, and also, as a novel non‐invasive biomarker for NAFLD diagnosis.

Background and AimsLittle is known about the extent of mitochondrial respiratory chain (MRC) activity dysfunction in patients with alcoholic hepatitis (AH). We aimed to assess the hepatic MRC activity in AH patients and its potential impact on the severity and prognosis of this life-threatening liver disease. MethodsMRC complexes were measured in liver biopsies of 98 AH patients (non-severe, 17; severe, 81) and in 12 histologically normal livers (NL). Severity was assessed according to Maddrey's Index and MELD score. Corticosteroid response rate and cumulative mortality were also evaluated. ResultsThe activity of the five MRC complexes was markedly decreased in the liver of AH patients compared with that of NL subjects, being significantly lower in patients with severe AH than in those with non-severe AH. There was a negative correlation between the activity of all MRC complexes and the severity of AH. Interestingly, only complex I and III activities showed a significant positive correlation with the corticosteroid response rate and a significant negative correlation with the mortality rate at all-time points studied. In a multivariate regression analysis, besides the MELD score and the corticosteroid response rate, complex I activity was significantly associated with 3-month mortality (OR = 6.03; p = 0.034) and complex III activity with 6-month mortality (OR = 4.70; p = 0.041) in AH patients. ConclusionOur results indicate that MRC activity is markedly decreased in the liver of AH patients, and, particularly, the impairment of MRC complexes I and III activity appears to have a significant impact on the clinical outcomes of patients with AH.

Low serum folate levels are inversely related to metabolic associated fatty liver disease (MAFLD). The role of the folate transporter gene (SLC19A1) was assessed to clarify its involvement in lipid accumulation during the onset of MAFLD in humans and in liver cells by genomic, transcriptomic, and metabolomic techniques. Genotypes of 3 SNPs in a case-control cohort were initially correlated to clinical and serum MAFLD markers. Subsequently, the expression of 84 key genes in response to the loss of SLC19A1 was evaluated with the aid of an RT² profiler-array. After shRNA-silencing of SLC19A1 in THLE2 cells, folate and lipid levels were measured by ELISA and staining techniques, respectively. In addition, up to 482 amino acids and lipid metabolites were semi-quantified in SLC19A1-knockdown (KD) cells through ultra-high-performance liquid chromatography coupled with mass spectrometry. SNPs, rs1051266 and rs3788200, were significantly associated with the development of fatty liver for the single-marker allelic test. The minor alleles of these SNPs were associated with a 0.6/−1.67-fold decreased risk of developing MAFLD. When SLC19A1 was KD in THLE2 cells, intracellular folate content was four times lower than in wild-type cells. The lack of functional SLC19A1 provoked significant changes in the regulation of genes associated with lipid droplet accumulation within the cell and the onset of NAFLD. Metabolomic analyses showed a highly altered profile, where most of the species that accumulated in SLC19A1-KD-cells belong to the chemical groups of triacylglycerols, diacylglycerols, polyunsaturated fatty acids, and long chain, highly unsaturated cholesterol esters. In conclusion, the lack of SLC19A1 gene expression in hepatocytes affects the regulation of key genes for normal liver function, reduces intracellular folate levels, and impairs lipid metabolism, which entails lipid droplet accumulation in hepatocytes.

Background: Non-alcoholic fatty liver disease (NAFLD) is the commonest cause of chronic liver disease worldwide, being non-alcoholic steatohepatitis (NASH) its most clinically relevant form. Given the risks associated with taking a liver biopsy, the design of accurate non-invasive methods to identify NASH patients is of upmost importance. BMP2 plays a key role in metabolic homeostasis; however, little is known about its involvement in NAFLD onset and progression. This study aimed to elucidate the impact of BMP2 in NAFLD pathophysiology. Methods: Hepatic and circulating levels of BMP2 were quantified in serum and liver specimens from 115 biopsy-proven NAFLD patients and 75 subjects with histologically normal liver (NL). In addition, BMP2 content and release was determined in cultured human hepatocytes upon palmitic acid (PA) overload. Results: We found that BMP2 expression was abnormally increased in livers from NAFLD patients than in subjects with NL and this was reflected in higher serum BMP2 levels. Notably, we observed that PA upregulated BMP2 expression and secretion by human hepatocytes. An algorithm based on serum BMP2 levels and clinically relevant variables to NAFLD showed an AUROC of 0.886 (95%CI, 0.83–0.94) to discriminate NASH. We used this algorithm to develop SAN (Screening Algorithm for NASH): a SAN < 0.2 implied a low risk and a SAN ≥ 0.6 indicated high risk of NASH diagnosis. Conclusion: This proof-of-concept study shows BMP2 as a new molecular target linked to NAFLD and introduces SAN as a simple and efficient algorithm to screen individuals at risk for NASH.