Effects of postprandial plasma and chylomicrons on endothelial cells. Differences between dietary cream and cod liver oil

Delayed clearance of triglyceride-rich lipoproteins in young, healthy obese subjects

Obesity is associated with the metabolic syndrome. The aims were, first, to study the postprandial triglyceride clearance in young, healthy obese subjects and, second, to investigate if fasting triglycerides can predict delayed postprandial triglyceride clearance. Eighteen apparently healthy, obese subjects with no clinical signs of metabolic disturbances participated. Controls were age- and sex-matched, healthy, normal weight subjects. Subclinical markers of metabolic disturbances were assessed by measuring postprandial triglycerides in serum and in chylomicrons by oral fat tolerance test. Postprandial triglyceride clearance for 8 h was assessed indirectly as removal of the lipid from serum during the oral fat tolerance test. Insulin resistance was measured by the homeostasis model assessment of insulin resistance (HOMA-IR). Twelve (66%) of the apparently healthy obese individuals had insulin resistance measured by HOMA-IR. There was a delayed clearance of serum triglycerides and chylomicron triglycerides at 6 h when compared with the control group, while, at 8 h, the differences were only detected for the chylomicron triglyceride clearance. Triglyceride response was significantly greater in the obese subjects. Fasting triglycerides in upper normal level predicted a delayed postprandial triglyceride clearance and insulin resistance. In young, apparently healthy obese subjects early metabolic disturbances including insulin resistance and delayed postprandial triglyceride clearance can be detected. Fasting serum triglyceride in upper normal level predicted delayed postprandial triglyceride clearance and insulin resistance.

Association of prothrombin and protein S with plasma triglyceride-rich lipoproteins in humans after test meals rich in milk fat or soybean oil

INTRODUCTION

Prothrombin can associate with rat chylomicrons in vitro. This enhances a platelet factor Xa mediated prothrombin activation when the chylomicron-prothrombin complex is exposed to platelets. Vitamin K-dependent pro- and anti-coagulation proteins are associated with TG-rich lipoproteins obtained from human plasma. In the present study, we examined the effects of saturated and unsaturated fat meals on the association of prothrombin and protein S with TG-rich lipoproteins in vivo.

MATERIALS AND METHODS

Human EDTA plasma was separated from normal subjects after overnight fasting and 2.5 h after ingestion of either a saturated fat meal (butter and cream) or an unsaturated fat meal (soybean oil) containing 54-80 g fat (60.2 E%). The prothrombin and protein S in delipidated lipoproteins were determined by SDS-PAGE combined with Western blotting.

RESULTS

Both prothrombin and protein S associated with TG-rich lipoproteins in fasting and in postprandial samples. The levels of prothrombin and protein S in postprandial TG-rich lipoproteins, especially after ingestion of a saturated fat meal, were higher than those in fasting TG-rich lipoproteins.

CONCLUSIONS

The levels of both prothrombin and protein S in TG-rich lipoproteins in plasma increased after a single fat meal. This association is more pronounced after saturated fat meals and one may hypothesize that it can be linked to atherogenic properties of TG-rich lipoproteins.

Lipid peroxidation of isolated chylomicrons and oxidative status in plasma after intake of highly purified eicosapentaenoic or docosahexaenoic acids

Fourteen healthy male volunteers were given two separate high-saturated-fat meals with and without the addition of 4 g highly purified ethyl esters of either eicosapentaenoic acid (EPA) (95% pure, n = 7) or docosahexaenoic acid (DHA) (90% pure, n = 7) supplied as 1-g capsules each containing 3.4 mg vitamin E. The chylomicrons were isolated 6 h after the meals, at peak concentrations of n-3 fatty acids (FA). Addition of n-3 FA with the meal caused a 10.4-fold increase in the concentration of n-3 FA in chylomicrons compared to the saturated fat meal without addition of n-3 FA. After the saturated-fat meal, the concentration of thiobarbituric acid-reactive substances (TBARS) was 327.6 +/- 34.6 nmol/mmol triacylglycerol (TAG), which increased to 1015.8 +/- 212.0 nmol/mmol TAG (P < 0.0001, n = 14) after EPA and DHA were added to the meal. There was no significant correlation between the concentrations of TBARS and vitamin E in the chylomicrons collected 6 h after the test meal. The present findings demonstrate an immediate increase in chylomicron peroxidation ex vivo provided by intake of highly purified n-3 FA. The capsular content of vitamin E was absorbed into chylomicrons, but the amount of vitamin E was apparently not sufficient to protect chylomicrons against lipid peroxidation ex vivo. Daily intake of 4 g n-3 FA either as EPA or DHA for 5 wk did not change the plasma concentration of TBARS. Although not significantly different between groups, DHA supplementation decreased total glutathione in plasma (P < 0.05) and EPA supplementation increased plasma concentration of vitamin E (P < 0.05). The other lipid-soluble and polar antioxidants in plasma remained unchanged during 5 wk of intervention with highly purified n-3 FA.

Effects of highly purified eicosapentaenoic acid and docosahexaenoic acid on fatty acid absorption, incorporation into serum phospholipids and postprandial triglyceridemia

Fourteen healthy volunteers were randomly allocated to receive 4 g highly purified ethyl esters of eicosapentaenoic acid (EPA) (95% pure, n = 7) or docosahexaenoic acid (DHA) (90% pure, n = 7) daily for 5 wk in supplement to their ordinary diet. The n-3 fatty acids were given with a standard high-fat meal at the beginning and the end of the supplementation period. EPA and DHA induced a similar incorporation into chylomicrons which peaked 6 h after the meal. The relative uptake of EPA and DHA from the meal was > 90% compared with the uptake of oleic acid. During absorption, there was no significant elongation or retroconversion of EPA or DHA in total chylomicron fatty acids. The concentration of EPA decreased by 13% and DHA by 62% (P < 0.001) between 6 and 8 h after the meal. During the 5-wk supplementation period, EPA showed a more rapid and comprehensive increase in serum phospholipids than did DHA. DHA was retroconverted to EPA, whereas EPA was elongated to docosapentaenoic acid (DPA). The postprandial triglyceridemia was suppressed by 19 and 49% after prolonged intake of EPA and DHA, respectively, indicating that prolonged intake of DHA is equivalent to or even more efficient than that of EPA in lowering postprandial triglyceridemia. This study indicates that there are metabolic differences between EPA and DHA which may have implications for the use of n-3 fatty acids in preventive and clinical medicine.

Effects of plasma on PGI2 release from prolonged perfused canine veins

Prostacyclin release from endothelial cells in culture appears increased by the presence of plasma, but occurrence of a similar phenomenon in intact vessels has not been established. In the present investigation release of 6-keto-PGF1 alpha, the stable breakdown product of prostacyclin, was quantitated from canine veins perfused ex vivo for 15 minute periods, using three different perfusates: 1) Hank's balanced salt solution (HBSS), 2) 20% platelet poor plasma (PPP) derived from heparinized blood, in HBSS, and 3) 20% PPP in HBSS with added arachidonic acid (AA). No differences in initial 6-keto-PGF1 alpha release existed among the three perfusates. However, PPP and PPP + AA solutions were associated with lesser declines in release, than occurred with HBSS alone, these differences being statistically significant after 60 min of perfusion (p less than 0.05). When PPP derived from heparinized and citrated blood rather than from only heparinized blood was used, there was a significantly lower release of prostacyclin (p less than 0.05). The latter may be due to citrate binding of calcium. These data indicate that autologous plasma does not alter initial prostacyclin release from freshly harvested canine veins, but that it weakens the decline in release usually following prolonged periods of perfusion.

Platelet activation by plasma lipoproteins

Enhanced platelet activity in patients with hypercholesterolemia and moderate hypertriglyceridemia can be attributed to increased LDL and VLDL and/or decreased HDL concentrations. In marked hypertriglyceridemia, where there is an accumulation of chylomicrons, platelet function is reduced. Treatment, whether by diet, medication, or plasmapheresis, that will result in a change in lipoprotein pattern is accompanied by a parallel change in platelet responsiveness. Incubation of lipoproteins with isolated platelets results in enhancement of platelet activation by LDL and VLDL and suppression of activity by HDL and chylomicrons. These findings have in vivo confirmation. They are even more pronounced and sometimes altered when the lipoproteins are derived from hyperlipidemic subjects. The effects of the lipoproteins on platelet activity appear to be dependent on lipoprotein composition and on factors such as cholesterol:protein ratio, apo C-III0:apo C-III2 ratio, apo B concentration, and triglyceride:protein ratio. The lipoproteins interact with platelets at specific receptor sites. Rapid change in platelet composition, particularly with regard to cholesterol, phospholipid, and fatty acid content, might ensue, with consequent alterations in membrane fluidity and enzyme activities and either suppression or activation of platelet function. This review has indicated that lipoproteins have a clear influence on platelet function. This interaction could be well of paramount importance in determining atherogenic risk.