Nonalcoholic Fatty Liver Disease Patients Exhibit Reduced CD47 and Increased Sphingosine, Cholesterol, and Monocyte Chemoattractant Protein-1 Levels in the Erythrocyte Membranes.

Abstract

Background: Nonalcoholic fatty liver disease (NAFLD) constitutes a significant cause of deaths, liver transplantations, and economic costs worldwide. Despite extended research, investigations on the role of erythrocytes are scarce. Red blood cells from experimental animals and human patients with NAFLD present phosphatidylserine exposure, which is then recognized by Kupffer cells. This event leads to erythrophagocytosis and amplification of inflammation through iron disposition. In addition, it has been shown that erythrocytes from NAFLD patients release the chemokine monocyte chemoattractant protein-1 (MCP1), leading to increased tumor necrosis factor alpha release from macrophages RAW 264.7. However, erythrophagocytosis can also be caused by reduced CD47 levels. Moreover, increased MCP1 release could be either signal-induced or caused by higher MCP1 levels on the erythrocyte membrane. Finally, erythrocyte efferocytosis could provide additional inflammatory metabolites. Methods: In this study, we measured the erythrocyte membrane levels of CD47 and MCP1 by enzyme-linked immunosorbent assay, and cholesterol and sphingosine with thin-layer chromatography. Eighteen patients (8 men and 10 women, aged 56.7 ± 11.5 years) and 14 healthy controls (7 men and 7 women, aged 39.3 ± 15.6 years) participated in our study. Results: The erythrocyte CD47 levels were decreased in the erythrocyte membranes of NAFLD patients (844 ± 409 pg/mL) compared with healthy controls (2969 ± 1936 pg/mL) with P = 0.012. Levels of MCP1 increased in NAFLD patients (389 ± 255 pg/mL) compared with healthy controls (230 ± 117 pg/mL) with P = 0.0274, but low statistical power. Moreover, in erythrocyte membranes, there was a statistically significant accumulation of sphingosine and cholesterol in NAFLD patients compared with healthy controls. Conclusions: Our results imply that erythrocytes release chemotactic "find me" signals (MCP1) while containing reduced "do not eat me" signals (CD47). These molecules can lead to erythrophagocytosis. Next, increased "goodbye" signals (sphingosine and cholesterol) could augment inflammation by metabolic reprogramming.