Oxidative-stress induced increase in circulating fatty acids does not contribute to phospholipase A2-dependent appetitive long-term memory failure in the pond snail Lymnaea stagnalis
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Abstract:
Reactive oxygen species (ROS) are essential for normal physiological functioning of the brain. However, uncompensated increase in ROS levels may results in oxidative stress. Phospholipase A2 (PLA2) is one of the key players activated by elevated ROS levels resulting in the hydrolysis of various products from the plasmamembrane such as peroxidized fatty acids. Free fatty acids (FFAs) and fatty acid metabolites are often implicated to the genesis of cognitive impairment. Previously we have shown that age-, and experimentally induced oxidative stress causes PLA2-dependent long-term memory (LTM) failure in an aversive operant conditioning model in Lymnaea stagnalis. In the present study, we investigate the effects of experimentally induced oxidative stress and the role of elevated levels of circulating FFAs on LTM function using a non-aversive appetitive classical conditioning paradigm.We show that intracoelomic injection of exogenous PLA2 or pro-oxidant induced PLA2 activation negatively affects LTM performance in our learning paradigm. In addition, we show that experimental induction of oxidative stress causes significant temporal changes in circulating FFA levels. Importantly, the time of training coincides with the peak of this change in lipid metabolism. However, intracoelomic injection with exogenous arachidonic acid, one of the main FFAs released by PLA2, does not affect LTM function. Moreover, sequestrating circulating FFAs with the aid of bovine serum albumin does not rescue pro-oxidant induced appetitive LTM failure.Our data substantiates previous evidence linking lipid peroxidation and PLA2 activation to age- and oxidative stress-related cognitive impairment, neuronal dysfunction and disease. In addition however, our data indicate that lipid peroxidation induced increased levels of circulating (per)oxidized FFAs are not a factor in oxidative stress induced LTM impairment.Keywords:
Lymnaea stagnalis
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This study investigated the effects of 9t18:1 (representing I-TFAs), 9t16:1, and 11t18:1 (representing R-TFAs) and their mixtures on the normal human hepatocyte LO2 cell function, the possible mechanism of lipid metabolism by lipidomics, and the relationship between phospholipase A2 (PLA2) and the arachidonic acid (AA) metabolic pathway. Here, we found that the damaging effect of 9t18:1 on the LO2 cell function was significantly greater than those of 11t18:1 and 9t16:1 (p < 0.05), and the damaging effects of CHB and HSO were significantly greater than those of HHB and CM (p < 0.05). The lipidomic results showed that TFAs and TFA mixtures caused a significant change in the lipid profiles of LO2 cells, in which the TAG, PL, and OL contents increased significantly. Moreover, 9t18:1 regulated only the protein expression of cPLA2 but did not participate in the AA metabolic pathway, while 11t18:1 and 9t16:1 participated in the COX-2 and CYP450 pathways, respectively.
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