Role of intracellular calcium and phospholipase A2 in arachidonic acid-induced toxicity in liver cells overexpressing CYP2E1

Abstract

Liver cells (HepG2 and primary hepatocytes) overexpressing CYP2E1 and exposed to arachidonic acid (AA) were previously shown to lose viability together with enhanced lipid peroxidation. These events were blocked in cells pre-incubated with antioxidants (α -tocopherol, glutathione ethyl ester), or in HepG2 cells not expressing CYP2E1. The goal of the current study was to evaluate the role of calcium and calcium-activated hydrolases in these CYP2E1-AA interactions. CYP2E1-expressing HepG2 cells treated with AA showed an early increase in cytosolic calcium and partial depletion of ionomycin-sensitive calcium stores. These changes in calcium were blocked by α -tocopherol. AA activated phospholipase A2 (PLA2) in CYP2E1-expressing liver cells, and this was inhibited by PLA2 inhibitors or α -tocopherol. PLA2 inhibitors prevented the cell death caused by AA, without affecting CYP2E1 activity or lipid peroxidation. AA toxicity and PLA2 activation were inhibited in calcium-depleted cells, but not by removal of extracellular calcium alone. Removal of extracellular calcium inhibited the early increase in cytosolic calcium caused by AA. CYP2E1 overexpressing HepG2 cells exposed to AA showed a decrease in mitochondrial membrane potential, which was prevented by the PLA2 inhibitors. These results suggest that AA-induced toxicity to CYPE1-expressing cells: (i) is associated with release of Ca 2+ from intracellular stores that depends mainly on oxidative membrane damage; (ii) is associated with activation of PLA2 that depends on intracellular calcium and lipid peroxidation; iii) does not depend on increased influx of extracellular calcium, and iv) depends on the effect of converging events (lipid peroxidation, intracellular calcium, activation of PLA2) on mitochondria to induce bioenergetic failure and necrosis. These interactions may play a role in alcohol liver toxicity, which requires polyunsaturated fatty acids, and involves induction of CYP2E1.

Impact of Selenium on the Leukotriene B4 Synthesis Pathway during Isoproterenol-Induced Myocardial Infarction in Experimental Rats

“…But, the animals that were pretreated with Se and then induced to have MI did not show much variations in these parameters when compared with the control group. Our results are in agreement with the earlier studies that have also shown that increased calcium derived from intracellular stores activates phospholipases, which, in turn, increases membrane damage through phospholipid hydrolysis [37].…”

STIM1 regulates calcium signaling in taste bud cells and preference for fat in mice

“…Besides, in vascular endothelial cells, laminar flow has been shown to induce both CD36 expression and activation of iPLA 2 (29). Furthermore, LAinduced activity of sPLA 2 and cPLA 2 was increased in the presence of Ca 2+ in the extracellular medium, as shown elsewhere (30)(31)(32) (34). Together, these observations suggest that CD36-positive cells possess the three PLA 2 isoforms actively implicated in the catalysis of AA.…”

Cystic Fibrosis-Related Oxidative Stress and Intestinal Lipid Disorders

“…The elevation of intracellular calcium is closely associated with phospholipase A2 (PLA2) activation that increases the release of AA from cell membranes, which contributes to the rise in EFA imbalance reported in CF. Indeed, AA serves as a substrate for the lipoxygenase system, conducting to raised ROS generation, lipid peroxidation, and eicosanoid synthesis, along with a fall in mitochondrial membrane potential, ATP production, and other oxidative damage to mitochondria (21,131,146). In the CF context, mitochondrial ROS overproduction is associated with marked depletion of GSH and redox imbalance (137).…”