Susceptibility of serum lipids to copper-induced peroxidation correlates with the level of high density lipoprotein cholesterol

NMR protocol for determination of oxidation susceptibility of serum lipids and application of the protocol to a chocolate study

A protocol for determination of oxidation susceptibility of serum lipids based on proton nuclear magnetic resonance ((1)H NMR) spectroscopy is presented and compared to the commonly used spectrophotometric method. Even though there are methodological differences between these two methods, the NMR-based oxidation susceptibility correlates well (r(2) = 0.73) with the lag time determined spectrophotometrically. In addition to the oxidizability of serum lipids, the NMR method provides also information about the lipid profile. The NMR oxidation assay was applied to the chocolate study including fasting serum samples (n = 45) from subjects who had consumed white (WC), dark (DC) or high-polyphenol chocolate (HPC) daily for 3 weeks. The oxidation susceptibility of serum lipids decreased in the HPC group, and there was a significant difference between the WC and HPC groups (P = 0.031). According to the random forest analysis, the consumption of the HPC chocolate induced changes to the amounts of HDL, phosphatidylcholine, sphingomyelin, and nervonic, docosahexaenoic and myristic acids. Furthermore, arachidonic, docosahexaenoic, docosapentaenoic and palmitic acids, gamma-glutamyl transferase, hemoglobin, HDL, phosphatidylcholine and choline containing phospholipids explained about 60% of the oxidation susceptibility values. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11306-011-0323-2) contains supplementary material, which is available to authorized users.

Acute myocardial infarction is associated with increased susceptibility of serum lipids to copper-induced peroxidation in vitro

BACKGROUND

Low-density lipoprotein (LDL) oxidation in the arterial intima plays a pivotal role in atherogenesis. Under physiologic conditions, several mechanisms protect LDL against oxidation, including hydrolysis of oxidation products by high-density lipoprotein (HDL)-associated enzymes. Some of these protective mechanisms are less effective under acute phase conditions.

HYPOTHESIS

Conditions of acute phase response, including acute myocardial infarction (MI), may be expected to result in increased susceptibility of serum lipids to oxidation. The present study was undertaken to test this possibility.

METHODS

Using our previously developed spectroscopic method, we have monitored prospectively the kinetics of copper-induced oxidation of serum lipids obtained from 15 men during and after acute MI. This was tested within 6 h from the onset of chest pain, on Days 1, 3, and 7 of infarction and 1 year after recovery.

RESULTS

The lag phase preceding oxidation of serum lipids was much shorter during the first week after MI when compared with values obtained after recovery (52-59 vs. 107 min, respectively, p <0.001). During the first week after MI, we observed no significant correlations between kinetic parameters and serum lipid composition, in contrast both to the correlations previously reported for hyperlipidemic patients and to the similar correlations observed in the present study after recovery.

CONCLUSIONS

Acute MI is associated with an increased susceptibility of serum lipids to oxidation in vitro. This propensity for oxidation may reflect enhanced in vivo formation of free radicals and/or reduced efficiency of defense mechanisms. Both these possibilities may carry detrimental effects on the course, complications, and prognosis of the patients after acute MI.

Serum lipid oxidizibility in term premature rupture of the membranes

OBJECTIVE

In our previous studies we have shown that the process of term labor is associated with oxidative stress, as indicated by increased susceptibility of maternal serum lipids to copper induced peroxidation. In order to continue evaluating the role of oxidative stress in the labor process, we next tested whether term premature rupture of the membranes (PROM) is also associated with increased susceptibility of maternal serum lipids to copper induced peroxidation.

DESIGN

A controlled prospective study.

SETTING

Tertiary care centre.

POPULATION

31 healthy women with term PROM and 19 healthy pregnant women with intact membranes. The women were matched for maternal and gestational age.

METHODS

Venous blood was drawn from the women (up to 6h after rupture of the membranes and prior to labor in the PROM group), and the kinetics of copper-induced oxidation of serum lipids ex vivo were monitored spectroscopically at 37 degrees C by continuous recording of absorbance at 245 nm.

RESULTS

The lag phase, reflecting resistance of serum lipids to oxidation, was similar in the PROM group when compared to the control group (43.7+/-3.2 versus 41.9+/-1.6 min, P=0.61). However, the maximal rate of oxidation (V(max)) and the maximal accumulation of absorbing products (OD(max)) were shorter in the PROM group when compared to the control group (5.14+/-0.26 versus 6.29+/-0.4010(-3) OD(245) nm/min, P=0.016; 0.61+/-0.03 versus 0.71+/-0.04 OD(245) nm, P=0.07).

CONCLUSION

As opposed to term labor, term PROM is not associated with increased maternal systemic oxidative stress when compared to normal pregnant women. The role for oxidative stress in preterm PROM warrants further studies.

Oxidative stress in the fetal circulation does not depend on mode of delivery

OBJECTIVE

We tested whether neonates are subject to oxidative stress by comparing the susceptibility of umbilical blood lipids with copper-induced peroxidation.

STUDY DESIGN

Umbilical arterial and venous blood samples were drawn from 32 pregnant women who delivered by elective cesarean section (CS) and from 32 pregnant women who delivered by spontaneous vaginal delivery (SVD) in a tertiary care center. Oxidative stress was evaluated by spectrophotometric monitoring of copper-induced peroxidation of serum samples.

RESULTS

The lag preceding lipid peroxidation in umbilical arterial blood was shorter than the lag in umbilical venous blood, irrespective of mode of delivery (14.0+/-1.8 vs 50.6+/-8.25 min, P=.0004 in SVD group; 17.7+/-1.6 vs 39.2+/-7.6 min, P=.006 in CS group).

CONCLUSION

Umbilical arterial lipids are more susceptible to peroxidation than umbilical venous lipids, indicating high oxidative stress in the fetal circulation irrespective of mode of delivery.

Preeclampsia is associated with increased susceptibility of serum lipids to copper-induced peroxidation in vitro

BACKGROUND

Several reports suggest preeclampsia to be associated with oxidative stress. In view of potential experimental artifacts in these studies, we tested the effect of preeclampsia on the oxidizibility of maternal serum lipids, using an optimized ex vivo method.

METHODS

This prospective study included 28 pregnant women with preeclampsia and 28 women matched for maternal and gestational age with normal pregnancies. Venous blood was drawn from the consenting women. Serum levels of lipid peroxidation products and the kinetics of copper-induced oxidation ex vivo were monitored spectroscopically by continuous recording of absorbance at 245 nm.

RESULTS

The initial optical density (OD) at 245 nm, attributed to preformed products of lipid peroxidation, was higher in the women with preeclampsia than in the controls (1.26 +/- 0.02 vs. 1.17 +/- 0.02 OD units; p = 0.01). The lag phase preceding oxidation, reflecting resistance of serum lipids to oxidation, was significantly shorter in the preeclampsia group than in the controls (47.4 +/- 2.3 vs. 57.6 +/- 4.0 min; p = 0.027).

CONCLUSIONS

High levels of serum hydroperoxides and increased susceptibility of serum lipids to copper-induced peroxidation ex vivo indicate preeclampsia to be associated with high oxidative stress. The role of this high oxidizibility in the pathogenesis of preeclampsia has yet to be evaluated.

Active labour is associated with increased oxidisibility of serum lipids ex vivo

OBJECTIVE

As a first step towards evaluating the role of oxidative stress in the process of labour, we tested whether term labour is associated with increased oxidisibility of maternal serum lipids.

DESIGN

A controlled prospective study.

SETTING

Tertiary care centre.

POPULATION

Twenty healthy women in active labour and 20 healthy pregnant women not in labour (controls) matched for maternal and gestational age.

METHODS

Venous blood was drawn from women in both groups. Serum levels of lipid peroxidation products and the kinetics of copper-induced oxidation ex vivo were monitored spectroscopically at 37 degrees C by continuous recording of absorbance at 245 nm.

MAIN OUTCOME MEASURES

Oxidative stress parameters.

RESULTS

The initial optical density (OD) at 245 nm, attributed to preformed dienic hydroperoxides and 7-keto-cholesterol (main products of lipid peroxidation), was higher in the labouring group than in the controls (1.30 +/- 0.11 vs 1.18 +/- 0.09, OD 245 nm, respectively, P < 0.001). The lag phase, reflecting resistance of serum lipids to oxidation, was significantly shorter in the labouring group than in the controls (43.2 +/- 1.4 vs 56.2 +/- 4.7 min, respectively, P = 0.01).

CONCLUSION

High levels of serum hydroperoxides and decreased resistance of serum lipids to copper-induced peroxidation ex vivo suggest labour to be associated with high oxidative stress. Whether oxidative stress is involved in initiating the labour process or is consequent awaits further studies.