Cytolysis does not per se induce lipid peroxidation: evidence in man

Macromolecular oxidation in anisotonic suspensions of mouse spleen cells

Macromolecular oxidative alterations have been analysed in vitro in anisotonic suspensions of mouse splenocytes. Both hypertonicity and hypotonicity induced the generation of thiobarbituric acid reactive species (TBARS) and carbonylation of the proteins, which took place along with cell death. Addition of antioxidants partially inhibited oxidative changes in isotonic and hypotonic suspensions. Anisotonic shock of mouse splenocytes proved to be an inducer of oxidative stress. The oxidative macromolecular alterations might contribute to pathogenesis of cell death caused by osmotic stress.

Pathogenesis of liver fibrosis: role of oxidative stress

In the liver, the progressive accumulation of connective tissue, a complex and dynamic process termed fibrosis, represents a very frequent event following a repeated or chronic insult of sufficient intensity to trigger a "wound healing"-like reaction. The fibrotic process recognises the involvement of various cells and different factors in bringing about an excessive fibrogenesis with disruption of intercellular contacts and interactions and of extracellular matrix composition. However, Kupffer cells, together with recruited mononuclear cells, and hepatic stellate cells are by far the key-players in liver fibrosis. Their cross-talk is triggered and favoured by a series of chemical mediators, with a prominent role played by the transforming growth factor beta. Both expression and synthesis of this inflammatory and pro-fibrogenic cytokine are mainly modulated through redox-sensitive reactions. Further, involvement of reactive oxygen species and lipid peroxidation products can be clearly demonstrated in other fundamental events of hepatic fibrogenesis, like activation and effects of stellate cells, expression of metalloproteinases and of their specific inhibitors. The important outcome of such findings as regards the pathogenesis of liver fibrosis derives from the observation of a consistent and marked oxidative stress condition in many if not all chronic disease processes affecting hepatic tissue. Hence, reactive oxidant species likely contribute to both onset and progression of fibrosis as induced by alcohol, viruses, iron or copper overload, cholestasis, hepatic blood congestion.

On the role of lipid peroxidation in the pathogenesis of liver damage induced by long-standing cholestasis

Previous studies have suggested a possible involvement of free radical reactions in the pathogenesis of cholestatic liver injury as well as in the modulation of hepatic fibrogenesis. In this study we investigated whether lipid peroxidation is involved in the development of chronic liver damage induced by long-standing cholestasis. For this purpose we have used the rat model of bile duct ligation (BDL), which leads to liver fibrosis and cirrhosis. Using this model we observed that the development of chronic liver damage was associated with the onset of lipid peroxidation, as pointed out by detection of carbonyl compounds, 4-hydroxynonenal (HNE) and malondialdehyde (MDA), in BDL livers and of fluorescent adducts between MDA and serum proteins. Lipid peroxidation was a relatively late event (starting after 1-2 weeks of BDL) and was unrelated to the early development of liver necrosis and cholestasis (already evident after 72 h after BDL). A positive significant linear correlation between the kinetic of infiltration of neutrophils and of a monocyte/macrophage population in BDL livers and MDA and HNE generation in the same organs is presented, indicating a close link between lipid peroxidation and the activation of inflammatory cells. We also observed that a positive linear correlation exists between collagen deposition in these livers and hepatic production of MDA and HNE. This event, which is accompanied by an increase in the number of fat storing cells (FSC, the cells that produce collagen in fibrotic liver), suggests that lipid peroxidation in this model may contribute to stimulate collagen synthesis by proliferating FSC.