Protection against liver ischemia–reperfusion injury in rats by silymarin or verapamil

Abstract

COMPLETE interruption of blood flow to the liver is sometimes necessary in liver surgery. Liver injury after cold or warm ischemia, followed by reperfusion, remains one of the major obstacles in liver surgery, especially in transplantation. A particularly important problem in liver transplantation, associated with ischemia–reperfusion injury, is primary nonfunction (PNF), which is the principal reason for retransplantation in the first 2 postoperative weeks. Various mechanisms have been implicated in liver ischemia–reperfusion injury, including reactive oxygen species generation, lipid peroxidation, alterations in calcium homeostasis, mitochondrial dysfunction, activation of Kupffer cells, and cytokine production. However, mechanisms that coordinate and integrate this pathologic response are still unclear. There is evidence that oxidative stress, defined as free radical production that exceeds the cellular antioxidant defense mechanisms, plays a major role in tissue injury. Some drugs that have properties of free radical scavengers and can prevent ischemia–reperfusion injury have been investigated. Silymarin, a flavonoid extract from the fruit Silybum marianum, with three isomers (silibinin, silidianin, and silicristin), has been shown to have protective properties, due to its ability to remove free radicals, prevent lipid peroxidation, prevent depletion of glutathione, and act as a scavenger of metal ions. Verapamil, a calcium channel blocker, acts as a protector of ischemia–reperfusion injury due to ability to prevent excessive accumulation of intracellular calcium, thus preserving mitochondria, function. A major problem in evaluating the efficacy of some drugs with potential antioxidant effects is finding reliable indexes of oxygen-derived free radical production, considering their high reactivity and short half-lives, and the accessibility of probes. This problem has been an obstacle to demonstrating a correlation between drug-induced liver protection and antioxident capacity. Enhanced luminescence has been used as an indirect, noninvasive method to assess oxygen radical formation. Studies in cultured cells have suggested that luminol, or lucigenin-amplified chemiluminescence can detect oxidative stress. Although the possible cytoprotective effect of silymarin and verapamil has been studied, there is no information about the comparative effects of these drugs-for over a short period of time in ischemia–reperfusion by methods that can evaluate antioxidant and cytoprotective capacity. We sought to determine whether the flavonoid compound, silymarin (S), or the calcium blocker, veraparnil (V), can protect against free radical generation and tissue injury.