No relationship between the age-related decrease in prostacyclin production and the level of intracellular lipid peroxidation in human umbilical vein endothelial cells in culture

Effects of exercise on platelet and aortic functions in aged rats

AIM AND METHODS

To assess age- and exercise-related changes in platelet aggregation, we measured the magnitude of platelet aggregation with a four-channel aggregometer, plasma and aortic polyunsaturated fatty acids by gas chromatography and related prostanoids with a reagent kit in young and aged non-exercised and in aged exercised rats.

RESULTS

Platelet aggregation in platelet-rich plasma induced by ADP (5 microm) in the primary wave increased with age. In the non-exercised groups, the basal levels of thromboxane B2 in platelet-rich plasma increased in aged rats compared with young rats. In aged exercised rats, the basal levels of 6-keto-prostaglandin F1alpha in platelet-rich plasma were stimulated and those of thromboxane B2 were depressed, compared with non-exercised aged rats. The plasma levels of eicosapentaenoic acid and docosahexaenoic acid increased with age. Only aortic eicosapentaenoic acid in the aged group increased by exercise. In the aged non-exercised and exercised groups, the aortic, but not the plasma, levels of eicosapentaenoic acid correlated inversely with the basal levels of thromboxane B2 in platelet-rich plasma (r = -0.53, P < 0.05) and associated negatively with the magnitudes of platelet aggregation induced by ADP (5 microm) (r = -0.47, P < 0.05).

CONCLUSION

These findings suggest that exercise in aged rats increases aortic eicosapentaenoic acid concentrations, which in turn depress the basal levels of thromboxane, B2 in platelet-rich plasma to modulate platelet aggregation.

The ratio of formation of prostacyclin/thromboxane A2 in HUVEC decreased in each subsequent passage

In this study, we analyzed the antioxidative potential (SOD-, GSH-Px-activity) and the basal, H2O2- and ATP-stimulated formation of PGI2 and TXA2 in human umbilical vein endothelial cells (HUVEC) of different passages. The subcultivation of cells partly represents the process of aging. Both subcultivation of the cells and the H2O2 incubation did not significantly influence the activity of SOD and GSH-Px. H2O2 (0.1 mM and 1.0 mM) stimulated the generation of PGI2 and TXA2 in the cell passages time dependently. The formation ratio of PGI/TXA2 changed from 640:1 (0.1 mM H2O2) or 430:1 (1.0 mM H2O2, 40 min incubation) at the 1st passage, to 13:1 and 17:1, respectively, at the 4th passage. This resulted from the reduction of the PGI2 synthesis connected with more pronounced TXA2 formation. The same behavior was found in the basal and ATP-stimulated eicosanoid formation. Based on this, the age-dependent activation of the oxygen radical formation could be responsible for the modified eicosanoid metabolism resulting in vascular complications in the elderly.

Elevated promotion of prostacyclin production by synthetic lipid A analogs in aged human endothelial cells in culture

We examined the effects of E. coli lipopolysaccharide (LPS) and synthetic analogs of lipid A, a bioactive moiety of LPS, on the prostacyclin (PGI2) production by young and old human endothelial cells in vitro. PGI2 production by endothelial cells has been shown to decrease during in vitro cellular senescence as well as in vivo. LPS and all the analogs tested in this study did not stimulate PGI2 production by young endothelial cells more than twofold. However, LPS and the majority of the lipid A analogs examined stimulated the PGI2 production by old cells more than twofold (approximately two- to sixfold). These results indicate that the responses to certain stimuli sometimes differ markedly between young and old cells, and this should be carefully considered when evaluating the biological effects of various compounds. Furthermore, these results suggest that certain synthetic lipid A analogs can be used as drugs to prevent some age-related vascular diseases.

A step in the process of prostacyclin production whose decline leads to the age-related decrease in production by human umbilical vein endothelial cells in culture

Human umbilical vein endothelial (HUVE) cells were examined at various culture ages for four steps of prostacyclin (PGI2) production ((1) incorporation of exogenous arachidonic acid into the cell membrane, (2) loss of arachidonic acid from the cell membrane to the cytoplasm, (3) conversion of arachidonic acid to PGI2 in the cytoplasm, (4) release of PGI2 to the outside of the cell) to determine the step whose decline leads to the age-related decrease in PGI2 production. Only conversion to PGI2 (step 3) showed the age-related decrease. Judging from these results, the authors conclude that the age-related decrease in PGI2 production is mainly due to the decrease in the ability of HUVE cells to convert arachidonic acid to PGI2 in the cytoplasm.

Epidermal growth factor suppresses in vitro senescence in the ability of human umbilical vein endothelial cells to proliferate, but not in the ability to produce prostacyclin

Addition of epidermal growth factor (EGF) to culture medium extended the replicative life span of human umbilical vein endothelial (HUVE) cells in culture. In brief, EGF suppresses the age-related decrease (in vitro senescence) in cell proliferative ability. However, the addition of EGF did not extend the culture period in which prostacyclin (PGI2) is actively produced by the cells. Therefore, EGF does not suppress the age-related decrease (in vitro senescence) in the ability of cultured HUVE cells to produce PGI2. These results suggest that the process of in vitro senescence in the cell proliferative ability is not necessarily correlated with that of in vitro senescence in the ability to produce PGI2.