Oxidative modification of high‐density lipoprotein 3 induced by human polymorphonuclear neutrophils

Abstract

The function of high-density lipoproteins (HDLs) in reverse cholesterol transport is impaired if HDLs are subjected to oxidative stress. Polymorphonuclear neutrophils (PMNs), which have been detected in the earliest stages of atherosclerotic lesions, are one of the most likely sources of the reactive oxygen species that cause such stress.In this study, we investigated the effect of a PMN oxidative burst on HDL3. We also studied the impact on these events of pentoxifylline, a drug that regulates granulocyte function.HDL3 (370 nmol´mL 21 cholesterol-HDL) was incubated with PMNs (2 £ 10 6´m L 21 ) in NaCl/P i in the presence or absence of an iron chelate complex (10 mm Fe-nitrilotriacetic acid) at 37 8C for 60 min or 24 h. Phorbol myristate acetate (PMA) or formyl-methionylleucyphenylalanine (fMetLeuPhe) was used to stimulate PMNs. In iron-free NaCl/P i medium, PMA-stimulated PMNs had a 40% lower HDL3 a-tocopherol content, whatever the incubation time. In NaCl/P i medium containing iron, there was 80% less HDL3 a-tocopherol at 60 min, and HDL3 atocopherol had almost disappeared after 24 h. In this latter condition, the amount of thiobarbituric acid-reactive substances was significantly higher than the respective control HDL3 (P , 0.05) and oxidation of HDL3 by PMAstimulated PMNs was associated with cross-linking of apoprotein AI, which was detected by SDS/PAGE. Similar results were obtained with fMetLeuPhe-stimulated PMN except that HDL3 a-tocopherol was consumed much more slowly during the first 60 min. Pretreatment of PMNs with various concentrations of pentoxifylline (0.001±20 mm) led to the concentration-dependent inhibition of oxidative modification of HDL3 induced by stimulated PMNs. The addition of 20 mm pentoxifylline in the most extreme oxidative stress conditions resulted in 70% of HDL3 atocopherol being maintained, with no formation of thiobarbituric acid-reactive substances and a lower level of apoprotein AI cross-linking.Thus HDL3 is susceptible to oxidative modifications induced by stimulated PMNs, in the presence of an exogenous source of iron. Pentoxifylline inhibited the oxidative modification of HDL3 by PMNs.

Human neutrophils employ the myeloperoxidase/hydrogen peroxide/chloride system to oxidatively damage apolipoprotein A‐I

“…At a molar phenylmethanesulfonyl fluoride : HOCl ratio of 20 (the highest phenylmethanesulfonyl fluoride concentration used) 95% of intact apo A‐I was recovered upon HOCl treatment versus 11% without phenylmethanesulfonyl fluoride addition. Thus, the presence of millimolar concentrations of phenylmethanesulfonyl fluoride as reported in [33,34] could suppress HOCl‐mediated apo A‐I fragmentation.…”

“…As we have obtained evidence that phenylmethanesulfonyl fluoride is a rather potent OCl − scavenger, we have used relatively low concentrations of phenylmethanesulfonyl fluoride to inhibit neutrophil‐derived proteases as compared to other studies (1 m m ; [33,34]). Treatment of apo A‐I with a fivefold molar excess of HOCl (18 µ m ) in the presence of increasing concentrations of phenylmethanesulfonyl fluoride (18–360 µ m ) led to a concentration‐dependent inhibition of apo A‐I fragmentation (Fig.…”

“…This highlights the caution with which such inhibitor studies should be performed in the presence of reactive compounds. Thus, the presence of millimolar concentrations of phenylmethanesulfonyl fluoride as reported in [33,34] could suppress HOCl-mediated apo A-I fragmentation and might be the reason for the apparent contradiction between the results of the present study and those reported by Cogny and colleagues [34]. A rough calculation from evidence obtained during the present study suggests that, under the experimental conditions applied here, approximately 50% of apo A-I was damaged via the MPO/H 2 O 2 /Cl 2 system, while about 25% of apo A-I damage can be ascribed to neutrophil proteases.…”

High Density Lipoproteins (HDL) and the Oxidative Hypothesis of Atherosclerosis

“…Two phenomena are involved in the capacity of native HDL to control the cholesterol efflux from cells. Pentoxifylline, a drug that regulates granulocyte function, is able to reduce the level of apo A-I cross-linking in HDL 3 incubated with these stimulated PMNs (81). The second process involves the intracellular cholesterol efflux and needs a specific binding of HDL to cells by means of the apolipoproteins (especially apo A-I).…”

Efecto de la pentoxifilina en la supervivencia, la función cardiaca y en la hemodinámica portal y sistémica de la cirrosis alcohólica avanzada: a randomized double-blind placebo-controlled trial

“…La pentoxifilina es un potente inhibidor de la síntesis del TNF-α con efecto antioxidante y antifibrogénico (18,19) que prolonga la supervivencia en pacientes con hepatitis alcohólica grave (20) y mejorar la función cardiaca y la supervivencia en pacientes con miocardiopatía dilatada (21).…”