In the present work the interrelations between cardiolipin (СL) and ceramide (CER) levels and functional state of the Wistar line rats’ tissues were investigated. It was shown that age-related or experimentally induced accumulation of CER is accompanied by a decrease in the level of CL in the heart, liver and brain of rats.
Various models for endogenous CER level elevation in cells and tissues of young animals have been used. Doxorubicin administration in young rats resulted in a CL content decrease in heart and addition of this drug to the hepatocytes incubation media resulted in a CL content decrease in liver cells of 3-month-old rats compared to control rats or cells. To determine if the observed CL reduction was referred to the CER accumulation, the modulators of CER cell metabolism – imipramine, GW4869 or myriocin – were used. It was found that inhibition of the CER de novo synthesis pathways by myriocin resulted in CL and phosphatidic acid content normalization in hepatocytes of 3-month-old rats.
In our work, the enrichment of the diet lipid component with saturated fatty acids from beef fat led to a decrease in CL content and to phosphatidic acid accumulation in tissues comparing with the rats received the standard diet. At the same time, diet caloric content limiting which is known to prevent CER content increase in aging cells, in turn, prevented CL levels reduction in heart, liver and brain of 24-month-old rats. In addition, intragastric ethanol administration to 3-month-old rats resulted in CL content decrease and fish oil n-3 polyunsaturated fatty acids or quercetin administration known to prevent CER accumulation prevented as well CL content reduction in heart and liver of ethanol-fed rats.
To prove the CER role in CL exchange and content modulation, exogenous natural and synthetic CER were used in model experiments in isolated cells. It was determined that hepatocytes incubation with exogenous CER caused CL level decrease in liver cells of 3-month-old rats. At the same time, C2-ceramide addition to hepatocyte incubation medium in 3-month-old rats` cells led both to CL level decrease and a drop in isotope-labeled linoleic acid inclusion to newly synthesized CL as well as increase in content of phosphatidic acid, which is phospholipid synthesis precursor. The obtained data indicate that CER content increase in the cell causes CL level decrease, via CL remodeling inhibition, which in turn can lead to cell death and liver pathologies development. At the same time, perfusion of hearts of young rats with C16-ceramide led to CL content decrease in heart muscle tissue, thus the relationship between the CER and CL content was revealed in the rat heart.
In order to reveal the role of endogenous brain CER in CL content age-related changes and brain functional state, the exogenous C16-ceramide effect on CL content in cortex and hippocampus of young rats was studied as well as brain functional state. For this purpose, young 3-month-old rats were given C16-ceramide by intranasal injection that led to CER level increase and CL content reduction in hippocampus, and emergence of some distinctive features in behavior of experimental rats such as increased anxiety, locomotor and research activity inhibition, and weakening of self-care instincts, which may indicate a depression-like state. At the same time, N-acetylcysteine (drug that reduces CER level by inhibiting neutral sphingomyelinase) administration in old rats led to CL level recovery and depressive-like behavior signs disappearance.
To determined how the age-related changes in CL content influences on the physiological state of cells, the effects of exogenous CL on affect target cells ability to response adequately insulin signal were studied. It was determined that exogenous CL introduction into the cell incubation medium of 24-month-old rat liver, cortex or calf muscle cells increased basal glucose absorption and glycogen synthesis as well as sensitivity of these cells to insulin. In model experiments on isolated liver cells, it was found that exogenous CL addition to hepatocytes incubation medium in 3-month-old rats after doxorubicin or C16-ceramide CER accumulation induction leads to an increase in basal and insulin-stimulated glucose uptake and glycogen synthesis. Thus, the obtained data suggest that age-related CL content changes may play an important role in reducing insulin sensitivity in classical target tissues and in brain.
