Cytokines play a very important role in nearly all aspects of inflammation and immunity. The term 'interleukin' (IL) has been used to describe a group of cytokines with complex immunomodulatory functions -- including cell proliferation, maturation, migration and adhesion. These cytokines also play an important role in immune cell differentiation and activation. Determining the exact function of a particular cytokine is complicated by the influence of the producing cell type, the responding cell type and the phase of the immune response. ILs can also have pro- and anti-inflammatory effects, further complicating their characterisation. These molecules are under constant pressure to evolve due to continual competition between the host's immune system and infecting organisms; as such, ILs have undergone significant evolution. This has resulted in little amino acid conservation between orthologous proteins, which further complicates the gene family organisation. Within the literature there are a number of overlapping nomenclature and classification systems derived from biological function, receptor-binding properties and originating cell type. Determining evolutionary relationships between ILs therefore can be confusing. More recently, crystallographic data and the identification of common structural motifs have led to a more accurate classification system. To date, the known ILs can be divided into four major groups based on distinguishing structural features. These groups include the genes encoding the IL1-like cytokines, the class I helical cytokines (IL4-like, γ-chain and IL6/12-like), the class II helical cytokines (IL10-like and IL28-like) and the IL17-like cytokines. In addition, there are a number of ILs that do not fit into any of the above groups, due either to their unique structural features or lack of structural information. This suggests that the gene family organisation may be subject to further change in the near future.

Aldehyde dehydrogenase 2 (ALDH2) is the major enzyme that metabolizes acetaldehyde produced from alcohol metabolism. Approximately 40-50% of East Asians carry an inactive ALDH2 gene and exhibit acetaldehyde accumulation after alcohol consumption. However, the role of ALDH2 deficiency in the pathogenesis of alcoholic liver injury remains obscure. In the present study, wild-type and ALDH2−/− mice were subjected to ethanol feeding and/or carbon tetrachloride (CCl4) treatment, and liver injury was assessed. Compared with wild-type mice, ethanol-fed ALDH2−/− mice had higher levels of malondialdehyde-acetaldehyde (MAA) adduct and greater hepatic inflammation, with higher hepatic interleukin (IL)-6 expression but surprisingly lower levels of steatosis and serum alanine aminotransferase (ALT). Higher IL-6 levels were also detected in ethanol-treated precision-cut liver slices from ALDH2−/− mice and in Kupffer cells isolated from ethanol-fed ALDH2−/− mice than those levels in wild-type mice. In vitro incubation with MAA enhanced the lipopolysaccharide (LPS)-mediated stimulation of IL-6 production in Kupffer cells. In agreement with these findings, hepatic activation of the major IL-6 downstream signaling molecule signal transducer and activator of transcription 3 (STAT3) was higher in ethanol-fed ALDH2−/− mice than in wild-type mice. An additional deletion of hepatic STAT3 increased steatosis and hepatocellular damage in ALDH2−/− mice. Finally, ethanol-fed ALDH2−/− mice were more prone to CCl4-induced liver inflammation and fibrosis than ethanol-fed wild-type mice. Conclusion : ALDH2−/− mice are resistant to ethanol-induced steatosis but prone to inflammation and fibrosis by way of MAA-mediated paracrine activation of IL-6 in Kupffer cells. These findings suggest that alcohol, by way of acetaldehyde and its associated adducts, stimulates hepatic inflammation and fibrosis independent from causing hepatocyte death, and that ALDH2-deficient individuals may be resistant to steatosis and blood ALT elevation, but are prone to liver inflammation and fibrosis following alcohol consumption. (Hepatology 2014;60:146–157)

Environmental Health Perspectives is an Open Access journal published by the National Institute of Environmental Health Sciences. Environmental Health Perspectives is an Open Access journal published by the National Institute of Environmental Health Sciences.

N² -ethylidene-2′-deoxyguanosine ( N² -ethylidene-dG) is a major DNA adduct induced by acetaldehyde. Although it is unstable in the nucleoside form, it is relatively stable when present in DNA. In this study, we analyzed three acetaldehyde-derived DNA adducts, N² -ethylidene-dG, N² -ethyl-2′-deoxyguanosine ( N² -Et-dG) and α-methyl-γ-hydroxy-1, N² -propano-2′-deoxyguanosine (α-Me-γ-OH-PdG) in the liver DNA of aldehyde dehydrogenase ( Aldh )- 2 -knockout mice to determine the influence of alcohol consumption and the Aldh2 genotype on the levels of DNA damage. In control Aldh2 +/+ mice, the level of N² -ethylidene-dG adduct in liver DNA was 1.9 ± 0.7 adducts per 10 ⁷ bases and was not significantly different than that of Aldh2 +/− and −/− mice. In alcohol-fed mice (20% ethanol for 5 weeks), the adduct levels of Aldh2 +/+, +/− and −/− mice were 7.9 ± 1.8, 23.3 ± 4.0 and 79.9 ± 14.2 adducts per 10 ⁷ bases, respectively, and indicated that adduct level was alcohol and Aldh2 genotype dependent. In contrast, an alcohol- or Aldh2 genotype-dependent increase was not observed for α-Me-γ-OH-PdG, and N² -Et-dG was not detected in any of the analyzed samples. In conclusion, the risk of formation of N² -ethylidene-dG in model animal liver in vivo is significantly higher in the Aldh2 -deficient population and these results may contribute to our understanding of in vivo adduct formation in humans.