Phospholipid synthetic and turnover pathways elicited upon exposure to different xenobiotics

Phospholipids, neutral lipids and glycolipids metabolism take the place during cell responses to different stimuli. Phospholipase and acyl glycerol lipase activities have been demonstrated to release second messengers that trigger cascade responses. Studies on lipid droplets structure, formation and interaction with other organelles have recently been described in prokaryotes and eukaryotes. Remodeling of membrane phospholipids has also been reported. NMR studies performed on synthetic membranes allowed to postulate membrane lipids polymorphism and to explain how processes like cell division, endocytosis and exocytosis can take place, due to special arrangements of the membranes. Studies from our research group on the pesticide dieldrin and Cu²⁺ effects through exposure of amphibian oocytes and embryos to sub-lethal and acclimation concentrations followed by toxic concentration challenges respectively, are discussed. Membrane phospholipids structure alterations allowing stabilization of bilayer arrangements were found for both stressors in cell and tissues. Metallothionein induction response that prevents oxidative stress was also found in acclimated embryo tissues. Probable connections between enzyme activities taking place on lysophospholipid and triacylglycerol substrates present in lipid droplets as well as phospholipid trafficking leading to modifications on membrane phospholipid ratios are discussed. Current new evidences in agreement with our findings allow us to suggest that our previously published results of dieldrin effects on amphibian cells correspond to joint coordinated activities, which probably had involved various metabolic pathways, in line with the acclimation experiment results and discussion. Independently of the cascade responses each toxicant is able to elicit, lipids play an important role in cell responses, both through rapid turnover and final stabilization of membrane bilayers.