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Role of free-radical reactions in liver diseases
J Fehér1, A Vereckei, G Lengyel
12nd Department of Medicine, Semmelweis University of Medicine, Budapest, Hungary.
Abstract:
Role of free-radical reactions is most significant in toxic liver injuries. Two traditional groups of liver injuries induced by drugs and chemicals are distinguished, 1. direct toxic type and 2. idiosyncratic type. Liver injury of direct toxic type is generally developed following toxin exposure, it is dose dependent, incubation period is short, and the injury often affects other organs (e.g. kidney). Direct toxins frequently cause typical zonal necrosis usually without concomitant signs of hypersensitivity. It is typical of idiosyncratic reaction that it appears only in a shorter period of exposure, it cannot be predicted, it is not dose-dependent, its incubation period varies and sometimes (in one-fourth of cases) it is accompanied by extrahepatic symptoms of hypersensitivity (fever, leukocytosis, eosinophilia, rashes), its morphologic picture shows great variety. A part of direct toxins is toxic itself, in the other part the basic compound is not toxic but it changes into toxic metabolites in the liver. Liver is well-protected against free-radicals developing in the organism: it is one of our best antioxidant supplied organs. It is probably due to the one of the important tasks of liver, namely detoxication of drugs, chemicals and toxic materials, with subsequent release of free-radicals. It is proved by the fact that in normal bile peroxidized lipids produced by free-radical chain reactions can also be detected. The pathologic free-radical reactions and one of their sequelae, peroxidation of lipids (LPO) do not necessarily cause cell and tissue damage. Antioxidant protection of cells and tissues is able to prevent free-radical injury and it enables, that the already developed damages become reversible. According to recent investigations, the lipid peroxidation, caused by free-radical reactions, or covalent binding of radical products to biomolecules does not lead directly to cellular destruction, only via further reactions. Such intermediary steps can be the phospholipase A2 activation, accumulation of lysophosphatides, poly-ADP-ribose polymerase repair enzyme activation, following oxidative damage of DNA, with subsequent NAD and ATP depletion. Its significance may be that the irreversible cellular and tissue damage can be prevented perhaps not only by administration of antioxidants, but also by compounds (e.g. phospholipase A2 inhibitors) affecting the above-mentioned biochemical mechanisms.
Insights
Free-radical reactions significantly contribute to toxic liver injuries. Novel therapeutic strategies may involve targeting biochemical mechanisms beyond antioxidants to prevent irreversible liver damage.
Area of Science:
- Hepatology
- Toxicology
- Biochemistry
Background:
- Free-radical reactions are central to toxic liver injuries, which are classified as direct or idiosyncratic.
- The liver possesses robust antioxidant defenses, essential for detoxifying drugs and chemicals, but free-radical generation during this process can lead to injury.
- Pathologic free-radical reactions and lipid peroxidation (LPO) do not always cause direct cellular damage due to endogenous antioxidant protection.
Purpose of the Study:
- To elucidate the role of free-radical reactions in toxic liver injury.
- To explore the mechanisms linking free-radical reactions to cellular damage.
- To identify potential therapeutic targets beyond traditional antioxidants.
Main Methods:
- Review of existing literature on toxic liver injury and free-radical mechanisms.
- Analysis of biochemical pathways involved in free-radical-induced liver damage.
- Investigation of intermediary steps leading to cellular destruction.
Main Results:
- Toxic liver injuries involve both direct and idiosyncratic reactions, with free radicals playing a significant role.
- The liver's antioxidant system combats free radicals, but detoxification processes can paradoxically generate them.
- Cellular damage from lipid peroxidation involves intermediary steps like phospholipase A2 activation and DNA repair enzyme activation, leading to energy depletion.
Conclusions:
- Irreversible liver damage may be preventable by targeting specific biochemical pathways, such as phospholipase A2 activation.
- Interventions affecting these intermediary mechanisms, in addition to antioxidants, could offer novel therapeutic approaches for toxic liver injury.