Alcohol, nutrition and liver cancer: role of Toll-like receptor signaling

Abstract

This article reviews the evidence that ties the development of hepatocellular carcinoma (HCC) to the natural immune pro-inflammatory response to chronic liver disease, with a focus on the role of Toll-like receptor (TLR) signaling as the mechanism of liver stem cell/progenitor transformation to HCC. Two exemplary models of this phenomenon are reviewed in detail. One model applies chronic ethanol/lipopolysaccharide feeding to the activated TLR4 signaling pathway. The other applies chronic feeding of a carcinogenic drug, in which TLR2 and 4 signaling pathways are activated. In the drug-induced model, two major methyl donors, S-adenosylmethionine and betaine, prevent the upregulation of the TLR signaling pathways and abrogate the stem cell/progenitor proliferation response when fed with the carcinogenic drug. This observation supports a nutritional approach to liver cancer prevention and treatment. The observation that upregulation of the TLR signaling pathways leads to liver tumor formation gives evidence to the popular concept that the chronic pro-inflammatory response is an important mechanism of liver oncogenesis. It provides a nutritional approach, which could prevent HCC from developing in many chronic liver diseases.

Figure 1

Main relationship between Toll-like receptor (TLR)2 and 4, their adaptors, protein kinases, which are linked to them and downstream signaling effects[26]. LPS: Lipopolysaccharide; LBP: LPS binding protein; CD14: Cluster of differentiation 14; ERK: Extracellular signal-regulated kinase; JNK: Jun N-terminal kinase; NF-κB: Nuclear factor κB; AP-1: Activator protein 1; TNF: Tumor necrosis factor.