Alcohol-associated liver disease (ALD) is a substantial cause of morbidity and mortality worldwide and represents a spectrum of liver injury beginning with hepatic steatosis (fatty liver) progressing to inflammation and culminating in cirrhosis. Multiple factors contribute to ALD progression and disease severity. Here, we overview several crucial mechanisms related to ALD end-stage outcome development, such as epigenetic changes, cell death, hemolysis, hepatic stellate cells activation, and hepatic fatty acid binding protein 4. Additionally, in this review, we also present two clinically relevant models using human precision-cut liver slices and hepatic organoids to examine ALD pathogenesis and progression.

Purpose: Both hepatic iron accumulation and hemolysis have been identified as independent prognostic factor in alcohol-related liver disease (ALD); however, the mechanisms still remain poorly understood. We here demonstrate that hepatocytes are able to directly ingest aged and ethanol-primed red blood cells (RBCs), a process termed efferocytosis. Methods: Efferocytosis of RBCs was directly studied in vitro and observed by live microscopy for real-time visualization. RBCs pretreated with either CuSO₄ or ethanol following co-incubation with Huh7 cells and murine primary hepatocytes. Heme oxygenase-1 (HO-1) and other targets were measured by q-PCR. Results: As shown by live microscopy, oxidized RBCs, but not intact RBCs, are rapidly ingested by both Huh7 cells and murine primary hepatocytes within 10 minutes. In some cases, more than 10 RBCs were seen within hepatocytes, surrounding the nucleus. RBC efferocytosis also rapidly induces HO1, its upstream regulator Nuclear factor erythroid 2-related factor 2 (Nrf2) and ferritin, indicating efficient heme degradation. Preliminary data further suggest that hepatocyte efferocytosis of oxidized RBCs is, at least in part, mediated by scavenging receptors such as ASGPR1. Of note, pretreatment of RBCs with ethanol but also heme and bilirubin also initiated efferocytosis. In a cohort of heavy human drinkers, a significant correlation of hepatic ASGPR1 with the heme degradation pathway was observed. Conclusion: We here demonstrate that hepatocytes can directly ingest and degrade oxidized RBCs through efferocytosis, a process that can be also triggered by ethanol, heme and bilirubin. Our findings are highly suggestive for a novel mechanism of hepatic iron overload in ALD patients.

Alcohol-related liver disease (ALD) and ALD-related mortality are associated with hemolysis, increased erythrophagocytosis, and disturbed iron homeostasis. While macrophage-mediated erythrophagocytosis is well established, we investigated the contribution of liver sinusoidal endothelial cells (LSECs) to handling oxidatively damaged or ethanol-primed red blood cells (RBCs) in ALD. Live-cell imaging demonstrated that damaged RBCs were rapidly taken up by SK-HEP1 cells, an endothelial cell line with LSEC-like characteristics, and RBC uptake was associated with induction of heme oxygenase-1 (HO-1) and activation of its upstream regulator Nrf2. siRNA-mediated knockdown of the scavenger receptor Stabilin-1 attenuated RBC-induced HO-1 expression, supporting a role for Stabilin-1 in efferocytic signaling. Exposure of RBCs to ethanol concentrations as low as 25 mM induced phosphatidylserine externalization and rendered erythrocytes efferocytosis-competent. Lysed RBCs and free hemin elicited comparable oxidative stress responses. In murine models of hemolysis and chronic ethanol feeding, hemoglobin-derived signals were detected within sinusoidal structures showing a diffuse CD206-positive distribution pattern consistent with the sinusoidal scavenger compartment. Similar signals were observed in sinusoidal endothelial regions in human heavy drinkers with clinical signs of hemolysis. Together, these data suggest that LSECs may represent an additional component of RBC clearance in ALD, alongside macrophages and hepatocytes, with implications for hepatic iron handling.