Adrenomedullin as an Immunomodulator of CD14⁺MerTK⁺ Circulating Monocytes in Liver Failure Syndromes

Liver failure syndromes are characterised by a dysregulated immune response leading to immune paralysis. Adrenomedullin (ADM) is a potent vasodilator and immunoregulator. This study aimed to explore the role of ADM in liver failure, hypothesising that there is a detrimental imbalance between ADM and adrenomedullin binding protein (AMBP)1 that promotes a switch of monocytes/macrophages towards a pro-restorative phenotype and function.

Consecutive patients with acute liver failure (ALF), acute-on-chronic liver failure (ACLF), and decompensated cirrhosis, as well as healthy controls (HC) were included between April 2020 and June 2024. Peripheral blood mononuclear cells/monocytes were isolated and used for RNA sequencing and cell culture. ADM and AMBP1 were measured by enzyme-linked immunosorbent assay.

Fifty-four patients with ALF, 25 with ACLF, 9 with decompensated cirrhosis, and 16 with HC were included. ADM expression in isolated monocytes was increased in ALF (log fold change = 5.88, p = 0.000216413) and ACLF (log fold change = 4.62, p = 0.00057122) compared to HC. Plasma ADM concentration was higher in ALF (1,684 ± 1,156 pg/mL) vs. ACLF (836.1 ± 765.2 pg/mL) and HC (164.8 ± 62.73 pg/mL). AMBP1 was significantly reduced in ALF (59.27 ± 44 µg/mL) vs. ACLF (126.3 ± 72.23 µg/mL) and HC (252.8 ± 159.7 µg/mL) (p < 0.0001, ALF vs. HC). Treatment with LPS increased ADM concentration in peripheral blood mononuclear cell supernatant (ALF n = 6; 561.4 ± 1,038 pg/mL vs. 259.2 ± 213.7 pg/mL, ACLF n = 4; 3,202 ± 491.2 vs. 1,757 ± 1,689 pg/mL). The percentage of CD14⁺ cells expressing Mer tyrosine kinase was reduced after culture with LPS (2.077 ± 0.87%); however, co-culture with ADM 100 nM restored the phenotype (3.852 ± 1.063%).

ADM is increased in liver failure, whereas AMBP1 is reduced. ADM affects monocyte function, increasing Mer Tyrosine Kinase and promoting a pro-restorative, anti-inflammatory phenotype.