Glycine but not gadolinium chloride or methyl palmitate reduces postischemic white blood cell accumulation and early graft nonfunction after liver transplantation in the rat

Glycine and glycine receptor signalling in non-neuronal cells

Glycine is an inhibitory neurotransmitter acting mainly in the caudal part of the central nervous system. Besides this neurotransmitter function, glycine has cytoprotective and modulatory effects in different non-neuronal cell types. Modulatory effects were mainly described in immune cells, endothelial cells and macroglial cells, where glycine modulates proliferation, differentiation, migration and cytokine production. Activation of glycine receptors (GlyRs) causes membrane potential changes that in turn modulate calcium flux and downstream effects in these cells. Cytoprotective effects were mainly described in renal cells, hepatocytes and endothelial cells, where glycine protects cells from ischemic cell death. In these cell types, glycine has been suggested to stabilize porous defects that develop in the plasma membranes of ischemic cells, leading to leakage of macromolecules and subsequent cell death. Although there is some evidence linking these effects to the activation of GlyRs, they seem to operate in an entirely different mode from classical neuronal subtypes.

Glycine blunts transplantative liver ischemia-reperfusion injury by downregulating interleukin 1 receptor associated kinase-4

AIM

To determine whether glycine could downregulate interleukin 1 receptor associated kinase-4 (IRAK-4) expression to interfere with lipopolysaccharides (LPS) signal transduction and blunt transplantative liver ischemia-reperfusion injury (I/RI).

METHODS

SD rats were randomly divided into two groups: donor animals of the glycine group (n=40) were given glycine (1.5 mL; 300 mmol/L, iv) 1 h before harvest, and the control group were treated with 1.5 mL physiological saline (n= 40). Orthotopic liver transplantation was then performed according to the Kamada technique. Ten animals in each group were followed up for 7 d after surgery to assess survival. The remaining animals in each group were divided into 3 subgroups (n=10) at 1h, 2 h and 6 h after portal vein reperfusion. Levels of LPS, serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) and total bilirubin in portal circulation, as well as IRAK-4 and TNF-alpha expression, NF-kappaB transcriptional activity and morphological study of liver tissues were analyzed.

RESULTS

Reperfusion resulted in a significant elevation of LPS concentrations in each group persisting to the end of our study. However, glycine, which led to improved survival rate and liver function, significantly alleviated liver parenchyma cell damage by downregulating IRAK-4, TNF-alpha expression and NF-kappaB transcriptional activity compared with the control group.

CONCLUSION

Glycine can attenuate hepatic I/RI by downregulating IRAK-4 to interfere with LPS signal transduction.

Methyl palmitate: inhibitor of phagocytosis in primary rat Kupffer cells

Kupffer cells are involved in phagocytosis and known to release biologically active mediators during early events of liver injury. Such functional properties of Kupffer cells can be modulated by methyl palmitate (MP). Therefore, efficacy of MP to modulate Kupffer cell function was evaluated in cultured primary Kupffer cells from rat liver. Phagocytic activity of Kupffer cells was measured by their capacity to phagocytize latex beads and the release of TNF-alpha, IL-10, IL-6, nitric oxide, and PGE2 was determined in cell culture medium after incubating the cells with various concentrations of MP for 24 h followed stimulation with lipopolysaccharide (LPS) for 6 h. To understand the mechanism of phagocytosis, we investigated the hydrolysis of MP, and determine ATP levels and activity of NF-kappaB in MP-inhibited Kupffer cells. A significant decrease was observed in phagocytosis. Phagocytosis evaluated at 0.5 mM MP was found to be time-dependent with a maximum decrease of 49% at 6 h. Exposure of Kupffer cells to MP followed by LPS stimulation showed a dose-dependent decrease in phagocytosis and reduced the release of TNF-alpha, IL-10, nitric oxide, and PGE2 but not of IL-6 levels in the supernatant as compared to the control. While ATP levels were unchanged, the nuclear factor NF-kappaB (p65) activity was inhibited in Kupffer cells treated with MP after LPS stimulation (35.6 RLU versus 49.6 RLU in control). Hydrolysis of MP was found to be time-dependent; maximum concentration of MP and palmitic acid (hydrolysis products) in the cell being at 3 and 6 h, respectively. In general, MP appears to reduce phagocytosis and levels of TNF-alpha, IL-10, nitric oxide, and PGE2 without affecting ATP levels and is probably mediated by NF-kappaB. This in vitro model is useful for detailed mechanistic studies of inhibition of phagocytosis by MP and other fatty acid esters.