Effect of infusion of a triacylglycerol emulsion on low-density lipoprotein composition and oxidizability

Influence of gestational age and birth weight in neonatal cholesterol response to total parenteral nutrition

BACKGROUND

Premature and critically ill infants receiving total parenteral nutrition (TPN) are at risk for dyslipidemia, and altered cholesterol levels in early life may contribute to later cardiovascular risk. Data regarding plasma cholesterol response to TPN in young infants are lacking.

OBJECTIVE

To determine the changes in plasma cholesterol levels during the first week of life in infants receiving TPN and a comparison group of infants who did not receive TPN during routine care.

METHODS

In a prospective, pilot cohort study, 38 neonates (30 TPN vs. 8 No-TPN) underwent serial blood sampling during the first week of life. Gas chromatography-mass spectrometry was used to measure cholesterol in plasma and TPN administered to study participants.

RESULTS

Baseline cholesterol level was similar between groups. In contrast to infants who did not receive TPN, cholesterol levels during the first week of life were significantly higher than baseline in infants receiving TPN (maximum cholesterol response 34% vs. 103% change from baseline, No-TPN vs. TPN, respectively, P = .036). After adjusting for cumulative cholesterol received by infants receiving TPN, maximum cholesterol response remained inversely related to gestational age and birth weight (P < .05).

CONCLUSION

Plasma cholesterol significantly increases during the first week of life in neonates receiving TPN. A higher cholesterol response was induced by TPN in infants of lower gestational age and birth weight.

Short-term exposure to exogenous lipids in premature infants and long-term changes in aortic and cardiac function

OBJECTIVE

Intravenous lipid use is associated with an acute hyperlipidemia, but long-term consequences have not been studied. We investigated whether elevated lipids in humans during the critical period of preterm neonatal life have a long-term impact on aortic and myocardial function relevant to adult disease.

METHODS AND RESULTS

We followed up 102 subjects born prematurely and now aged 23 to 28 years. Eighteen received intravenous lipids as neonates and were matched to controls with equivalent perinatal characteristics. Global and regional aortic stiffness and left ventricular function were assessed by cardiovascular magnetic resonance. Those who received intravenous lipids had greater aortic stiffness in early adulthood (P=0.0002), with greater stiffness in the abdominal aorta (P=0.012). The relationship was graded according to the elevation in neonatal cholesterol induced by intravenous lipids (P<0.0001) but not other metabolic parameters altered by the infusion. Peak systolic circumferential strain was also reduced in the lipid group (P=0.006), which, again, was proportional to neonatal cholesterol level (P<0.01).

CONCLUSIONS

Aortic and myocardial function in young adulthood is associated with intralipid exposure during neonatal life for preterm infants, in a graded manner related to the rise in cholesterol. Circulating cholesterol during critical developmental periods may have long-term impacts on the human cardiovascular system.

High resting triacylglycerol turnover of rainbow trout exceeds the energy requirements of endurance swimming

Fish may use lipoproteins instead of albumin-bound fatty acids to fuel endurance exercise, but lipoprotein kinetics have never been measured in ectotherms. In vivo bolus injections of labeled very-low-density lipoproteins (3H-VLDL labeled in vivo from donor fish) and continuous infusions of Intralipid (3H-labeled artificial emulsion) were used to investigate the effects of prolonged exercise (6 h at 1.5 body length/s) and heparin (600 U/kg) on the turnover rate of circulating triacylglycerol (TAG) in rainbow trout. We hypothesized that swimming would stimulate TAG turnover rate to fuel working muscles and that heparin would reduce flux by releasing lipoprotein lipase (LPL) from endothelial cells. Results from both tracer methods show that the baseline TAG turnover rate of trout ranges from 24 to 49 μmol TAG·kg−1·min−1and exceeds all values measured to date in endotherms. More important, this high resting turnover rate is not stimulated during swimming, because it can already cover several times the energy requirements of locomotion. The fact that heparin causes a 50% decrease in baseline TAG turnover rate suggests that fish LPL must be bound to the endothelium for normal tissue uptake of fatty acids supplied by lipoproteins, as in mammals. We propose that the high resting TAG turnover rate of rainbow trout could be needed by ectotherms for rapid restructuring of membrane phospholipids. The continuous tracer infusion method implemented here could be a versatile tool to investigate the potential role of lipoproteins in providing fatty acids for rapid homeoviscous adaptation.

LDL resistance to oxidation: Effects of lipid phenotype, autologous HDL and alanine

BACKGROUND

Although LDL resistance to copper-induced oxidation is a time-honoured method, how it is modulated by the physiologic variability of lipid phenotype and what influences the protective action of homologous HDL and exogenous alanine is still unclear.

METHODS

In 159 subjects without severe dyslipidemias, LDL resistance to copper-induced oxidation (lag phase) was measured under standardised conditions, with alanine and with autologous HDL.

RESULTS

Lag phase was normally distributed and averaged 68+/-10 min (range: 40-105 min). Both VLDL-triglycerides (37+/-5, 52+/-7, 59+/-7, 53+/-5 mg/dl, p<0.05) and LDL-triglycerides (27+/-2, 27+/-1, 30+/-2, 35+/-3 mg/dl, p<0.01) increased across quartiles of lag phase. The relative LDL enrichment in triglycerides (triglycerides percent or triglycerides/cholesterol ratio) was strongly related to lag phase (r=0.29 and r=0.31, p<0.0005 for both) independently of age, gender, BMI, and presence of diabetes or hypertension. The protective effect of HDL was variable (+42+/-18 min) and largely dependent on the capacity of HDL to resist oxidation (r=0.69, p<0.0001). Alanine induced a rather constant lag phase prolongation (+32+/-7 min) that was weakly related only to baseline lag phase (r=0.17, p<0.05).

CONCLUSIONS

Relative triglyceride abundance protects LDL from ex-vivo oxidation, HDL particles protect LDL mainly through substrate dilution and alanine probably through a direct anti-oxidant effect.

Long-term monounsaturated fatty acid diets reduce platelet aggregation in healthy young subjects

The aim of the present study was to compare the response of a range of atherogenic and thrombogenic risk markers to two dietary levels of saturated fatty acid (SFA) substitution with monounsaturated fatty acids (MUFA) in students living in a university hall of residence. Although the benefits of such diets have been reported for plasma lipoproteins in high-risk groups, more needs to be known about effects of more modest SFA-MUFA substitutions over the long term and in young healthy adults. In a parallel design over 16 weeks, fifty-one healthy young subjects were randomised to one of two diets: (1) a moderate-MUFA diet in which 16 g dietary SFA/100 g total fatty acids were substituted with MUFA (n 25); (2) a high-MUFA diet in which 33 g dietary SFA/100 g total fatty acids were substituted with MUFA (n 26). All subjects followed an 8-week run-in diet (reference diet), with a fatty acid composition close to the UK average values. There were no differences in plasma lipid responses between the two diets over 16 weeks of the study with similar reductions in total cholesterol (P<0.001) and LDL-cholesterol (P<0.01) in both groups; a small but significant reduction in HDL-cholesterol was also observed in both groups (P<0.01). Platelet responses to ADP (P<0.01) and arachidonic acid (P<0.05) differed with time on the two diets; at 16 weeks, platelet aggregatory response to ADP was significantly lower on the high-MUFA than the moderate-MUFA (P<0.01) diet; ADP responses were also significantly lower within this group at 8 (P<0.05) and 16 (P<0.01) weeks compared with baseline. There were no differences in fasting factor VII activity (factors VIIc and VIIag), fibrinogen concentration or tissue-type plasminogen activator activity between the diets. There were no differences in postprandial factor VIIc responses to a standard meal (area under the curve) between the diets after 16 weeks, but postprandial factor VIIc response was lower than on the high-MUFA diet compared with baseline (P<0.01). In conclusion, a high-MUFA diet sustains potentially beneficial effects on platelet aggregation and postprandial activation of factor VII. Moderate or high substitution of MUFA for SFA achieves similar reductions in fasting blood lipids in young healthy subjects.

Lipoproteins and low-dose estradiol replacement therapy in post-menopausal Type 2 diabetic patients: the effect of addition of norethisterone acetate

AIMS

Low-dose continuous oestrogen/progestogen may increase patient compliance long-term but the cardioprotective effects in diabetes are unknown. The aim of this study was to compare the effect of low-dose oral oestrogen (1 mg, 17-beta-estradiol) treatment with oestrogen (1 mg 17-beta-estradiol) in combination with low-dose (0.5 mg) continuous norethisterone acetate (NETA) on lipoproteins in Type 2 diabetic patients.

METHODS

Thirty-four post-menopausal Type 2 diabetic patients in moderate control (mean haemoglobin A1c 7.7%) who had a serum oestradiol level of < 50 pg/ml were examined over a 6-month period. Serum lipids, and lipoprotein composition of very low density lipoprotein (VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL) were measured. Serum lipoprotein(a) was determined by an ELISA method, LDL fatty acids by gas-liquid chromatography and LDL oxidizability by thiobarbituric acid reactive substances (TBARS assay). Cholesteryl ester transfer protein (CETP), and cell cholesterol were measured.

RESULTS

There was a reduction in serum cholesterol on both treatments but no significant difference between treatment groups. LDL cholesterol decreased by 17% in each group. There was a no significant difference between the groups in serum VLDL or HDL cholesterol or serum triglycerides during the study. The change in lipoprotein(a) during the study was not significantly different between the groups. There was no significant difference in 4 h LDL oxidizability between groups. Although CETP increased with time in both groups there was no significant difference in the change between the groups.

CONCLUSION

In this small study, the addition of continuous low-dose NETA did not reduce the potentially beneficial effects of low-dose 17-beta-estradiol on the progression of atherosclerosis in diabetes.

Evidence that acute insulin administration enhances LDL cholesterol susceptibility to oxidation in healthy humans

Increased free radical production and hyperinsulinemia are thought to play a role in experimental and human atherosclerosis, but the relation between the 2 abnormalities has not been studied. In 23 healthy volunteers, we measured the susceptibility of circulating low-density lipoprotein (LDL) cholesterol particles to in vitro copper sulfate oxidation (measured as the lag phase) and cell-mediated oxidative modification (measured as malondialdehyde generation in LDL during incubation with human umbilical vein endothelial cells), as well as the vitamin E content of LDL cholesterol at baseline and after 2 hours of physiological hyperinsulinemia (euglycemic insulin clamp). The lag time of LDL oxidation decreased from control values of 108+/-3 and 107+/-3 minutes (at baseline and after 2 hours of saline infusion) to 101+/-3 minutes after 2 hours of clamping (P<0.0001). At corresponding times, cell-mediated malondialdehyde generation in LDL rose from 4.96+/-0.11 and 4.98+/-0.10 to 5.28+/-0.10 nmol/L (P=0. 0006), whereas the LDL vitamin E content decreased from 6.78+/-0.06 and 6.77+/-0.06 to 6.64+/-0.06 microg/mg (P<0.04). The insulin-induced shortening of the lag phase was directly related to the decrement of vitamin E in LDL; furthermore, in subjects with higher baseline serum triglyceride levels, insulin induced a greater shortening of the lag phase than in subjects with low baseline triglycerides. We conclude that in healthy humans acute physiological hyperinsulinemia enhances the oxidative susceptibility of LDL cholesterol particles. This effect may have pathogenic significance for atherogenesis in insulin resistant states.