Transient loss of serum protective activity following short-term stress: a possible biochemical link between stress and atherosclerosis.

Very low density lipoproteins (VLDL) are toxic to aortic endothelial cells in vitro, and toxicity preventing activity (TxPA) inhibits this toxic effect of VLDL. Stress, an established arteriosclerosis risk factor, was examined for its effect on TxPA and on the ability of serum to protect endothelial cells from in vitro injury by VLDL. A standardized mirror tracing task with noise was administered to four healthy subjects. Blood samples were obtained at 0, 30, (stressor) 35, 50 and 80 min. Cortisol and non-esterified fatty acids increased during the stress period. TxPA significantly decreased following the stressor and had recovered by 80 min. When the ratio of non-TxPA/TxPA rose above 2, serum was no longer able to protect the cells from VLDL injury. If endothelial cells in vivo respond similarly to the endothelial cells in culture, the effect of stress on atherosclerosis may be mediated through these transient decreases in TxPA.

Effects of stress and blood type on cortisol and VLDL toxicity preventing activity.

Past research has associated ABO blood type and mental stress with cardiovascular risk. We studied the effects of blood type (A vs. O) coupled with a mirror drawing stressor on very low density lipoprotein toxicity-preventing activity (TxPA) and plasma cortisol levels. Exposure to the stressor significantly decreased TxPA and increased cortisol for the total group of 25 older adult males. However, the stress response patterns of the 15 blood type A males were different from those of the 10 type O subjects. The blood type A group had higher initial levels of TxPA and cortisol as well as quicker stress recovery rates than the type O group. ABO blood type may be an important behavioral hematologic variable to assess in studies concerning biochemical stress response or cardiovascular risk.

Aspirin improves the patency rate of seeded vena cava grafts.

The purpose of this study was to evaluate the effectiveness of aspirin (ASA) and porcine endothelial cell seeding in improving the patency rate of vena cava grafts. Thirty-nine dogs underwent infrarenal vena cava replacement by 10 cm lengths of 8 mm I.D. ringed polytetrafluoroethylene grafts. Thirty-one grafts were seeded with 1-1.5 x 10(6) porcine aortic endothelial cells while eight were not (GIII). Of the seeded group, 16 animals received no ASA (GI), while 15 others (GII) were given ASA (325 mg) daily starting two days preoperatively and continuing until sacrifice. Venograms were performed on the fourth postoperative day. Grafts were harvested 32 days after insertion and evaluated for patency rate and endothelialized surfaces. The 32-day patency rate was significantly higher for GII than for GI and III animals (67% vs. 13 and 25% respectively). Endothelialized surface was higher in GII than Gi and III (67% vs. 16% and 18% respectively). We conclude that endothelial cell seeding alone does not prevent graft closure and that a combination of ASA and cell seeding significantly increases the patency rate of vena cava grafts.

Stimulation of esterified cholesterol accumulation in tissue culture cells exposed to high density lipoproteins enriched in free cholesterol.

Human high density lipoprotein enriched in free cholesterol was obtained by exposing the lipoprotein to lipid dispersions having a free cholesterol/lecithin molar ratio greater than two. The metabolism of cholesterol was studied in tissue culture cells exposed to normal and cholesterol-enriched lipoproteins. Incubation of Fu5-AH rat hepatoma cells in medium containing cholesterol-enriched lipoprotein resulted in the accumulation of cellular cholesterol whereas normal high density lipoprotein produced no change in cellular content. The accumulated sterol was recovered primarily as esterified cholesterol and was derived almost entirely from lipoprotein free cholesterol. The esterification of incorporated free cholesterol and the cellular cholesterol content were directly related to the molar ratio of free cholesterol to phospholipid in the lipoprotein and to the concentration of lipoprotein in the culture medium. Isotopic experiments utilizing lipoprotein labeled with 125I or [4-14C]cholesteryl oleate demonstrated that a large fraction of the cholesterol incorporated from lipoprotein enriched in free cholesterol occurred by mechanisms that did not result in lipoprotein internalization and degradation. The response of other tissue culture cells to cholesterol/phospholipid dispersions is presented. The data indicate that the lipid composition of a lipoprotein can regulate free cholesterol uptake and esterification as well as cellular cholesterol content.

Cellular cholesterol ester accumulation induced by free cholesterol-rich lipid dispersions.

The influence of lipoprotein composition on free cholesterol (RC) esterification and accumulation of esterified cholesterol (EC) was studied in cells of Fu5AH rat hepatoma exposed to culture media supplemented with (FC/P) ranging from 0.6 to 2.8. In the presence of normal human serum, FC-lecithin dispersions witb a FC/P greater than one stimulated both the esterification of FC and the accumulation of cellular EC. Conversely, dispersions with FC/P values of approximately one had no effect on either FC esterification or the accumulation of EC when compared to cells grown in the absence of lipid dispersions. No stimulation of cellular response was obtained when FC-rich dispersions were added to cells in the absence of serum; however, stimulation was observed when cells were exposed to isolated human serum lipoproteins (very low density, low density, and high density). With each lipoprotein, FC-lecithin dispersions with FC/P values less than one inhibited cholesteryl ester accumulation, FC-rich dispersions stimulated, and dispersions with FC/P values of approximately one had an effect equivalent to that of isolated lipproteins alone. These studies extablish that cellular FC esterification and EC content are not influenced solely by the FC concentration of medium, but rather respond to the ratio of FC to phospholipidl These studies also suggest that serum lipoproteins participate in the transfer of FC carried by FC-rich lecithin dispersions to cells.

Preparation of delipidized serum protein for use in cell culture systems.

A rapid procedure for the preparation of delipidized serum protein is described. The delipidized protein can be used for the maintenance and growth of tissue culture cells in a lipid-free environment. The extraction procedure greatly reduces all serum lipid classes and the delipidized protein supports the growth of a variety of cells in culture.

Effect of inhibition of protein synthesis on lipid metabolism in Lactobacillus plantarum.

In Lactobacillus plantarum 17-5, lipid synthesis appears to be correlated with protein synthesis. Inhibition of protein synthesis by chloramphenicol (50 mug/ml) caused the nearly simultaneous inhibition of incorporation of radioactive oleic acid into polar lipids before the cessation of growth. In addition, de novo fatty acid synthesis, as determined by the incorporation of radioactive acetate into cellular lipids, was also inhibited. Removal of the antibiotic resulted in the resumption of growth, protein synthesis, and polar lipid synthesis. Inhibition of protein synthesis by leucine deprivation also produced a marked reduction in the incorporation of radioactive oleic acid into the total polar lipids at about the same time that growth stopped (30 to 60 min after the removal of leucine). However, the different classes of lipids behaved differently. For example, the incorporation of oleic acid into cardiolipin was inhibited immediately upon removal of leucine from the cultures, whereas incorporation into phosphatidyl-glycerol was maintained at near normal rates for 60 min after the removal of leucine and then ceased. In contrast, the accumulation of radioactive oleic acid in a neutral lipid identified as diglyceride occurred to a much greater extent in leucine-deprived cultures than in control (+ leucine) cultures. Upon addition of leucine to leucine-deprived cultures, the rates of synthesis of phosphatidyl-glycerol and cardiolipin returned to normal; the amount of radioactivity in the diglyceride fraction decreased to normal levels concomitantly with increased phospholipid synthesis.

Estrogen-dependent in vitro stimulation of RNA synthesis in hormone-dependent mammary tumors of the rat.

Incubation of estradiol in vitro at 25 degrees C with homogenates of carcinogen-induced mammary tumors of ovariectomized rats stimulated the magnesium-dependent RNA polymerase activity of nuclei of the hormone-dependent (HD) (regressing) tumors, but had no effect on this activity in nuclei of hormone-independent (HI) (growing) tumors. Furthermore, recombination of the nuclei and cytosol fractions of HD and HI tumors indicated that the in vitro effect of estradiol on subsequent tumor nuclear RNA synthesis required the estrogen receptor-containing cytosol but was specific to nuclei of the HD tumor. This constituted the first direct in vitro effect of estrogen on a specific biochemical process in an HD mammary tumor.