A protective role for nitric oxide in the oxidative modification of low density lipoproteins by mouse macrophages

Abstract

Low denfity lipoprot¢ins (LDL) oxidati~ly modified by maeropha~s have been shown to tm atherogeni¢ in ~ vivo studio, W= studied the potential role of nitric oxide (NO), a free r-adi~l produt:ed by maerophag=;, in LDL modifi~tion, Human LDL (I mg/ml) were incubated with mouse Ixritom:al ma¢rophag~ in Ham's F-IO medium. The ¢¢1ls w=r¢ then stimulat~ by interferon.y and tumor n¢¢rosi= fa=or-¢ to inerea~ their production of NO from t.3 to 12.2 tam in 24 h. us mcatsured by nitrite. Lipid l~roxidation of LDL, as m~sured by thio~rbitudc acid.tractive materials (";'BARS). was reduexd in stimulated c¢{l~ in a time.dependent manner. At 24 h, the d=rcar¢ ~s about 2"/%. In tl;¢ preu:n¢¢ of an NO syntha~ inhibitor (N".aminophomoarginin¢). the Ilcncration of NO was diminished and tim proration a~init LDL lipid pcroaidation wa~ reverted, The extent of LDL protein modifiemtion was al~ assessed by examining its electropho~tic mobility. It wall found that macrophage NO reduced the change in LDL ¢lectromobility, These data ladS=ate that the production of NO may inlfibit the oxidative modification of LDL with cytokine,stimulatcd macrophag¢*, We suggest that NO plays a protective role in limiting macrophage.indutu=d LDL modifl=ation, [15,16], In the presence of an antioxidant, such as probucol, the formation of foam ~lls is inhibited both in vitro and in vivo [17][18][19][20][21]. However, the sources and species of those free radicals responsible for the oxidation of LDL are not well established, The superoxid¢ anion (Of) produced by macrophages is known to be involve, sin~ the pretreatment of macrophages with superoxid¢ dismuta~e (SOD) attenuates LDL lipid peroxidation [22]. Macrophages have been shown to produce the nitric oxide (NO) radical via nitric oxide synthase. This enzyme converts arginine into citrulline and is indued by cytokin, treatment [23,24], Although NO can neutrali~ Oi-to form a stable peroxynitrit¢ anion (ONOO') [25], under some conditions th¢ peroxynitrit¢ can also rapidly decompose to form a strong oxidant with reactivity similar to the hydroxyl radical In addition. NO generation in vivo may lead to the mobilization of iron with a subsequent increase in the level of reactive oxygen slzt¢ics [2?]. These observation= could ¢~plain the cytotoxi¢ action of NO that has been demonstrated in a numL~r of studies [28,29]. The purpose of the present study was to dctermin, the ,ff~t of NO production by macrophagcs on LDL lipid [mroxi. datioa. To this end we incubated LDL with macrophages in which the synthesis of NO was induced with interf¢ron-7 and tumor necrosis factor-~, and followed the extent of oxidative modification of LDL. ,i, Nitric oxide .¢k.tztha~'e inhibitor (MDL lO0.24tt) $-Mcthylisothio~emi~ar "b~tde hydroio,Jid¢ (17,8 8. 0.0?fi tool) was added to L-ly£n¢ monohydrate (9,3 $, 0,076 tool) in water (t00 ml) and adjusted to pH 9.5 with I N NaOH, The r~gtion mi~tu~ wa= h~t~ and stirred at 40"C for 30 h. The solution was then cooled to room teml~rature and acidified to pH 4.0 with acetic acid. F~vianic acid (...

Nitric Oxide Regulation of Free Radical– and Enzyme-Mediated Lipid and Lipoprotein Oxidation

“…Murine peritoneal macrophages, having iNOS activity stimulated by interferon-␥ and lipopolysaccharide, are less capable of oxidizing LDL than are unstimulated macrophages. 36,37 This lipid protective effect can be reversed by addition of the NOS inhibitors N G -aminohomoarginine 36 and N G -monomethylarginine. 37 When exogenous ⅐ NO is added to unstimulated macrophages, oxidation of LDL is inhibited.…”

Oxygen-derived species: their relation to human disease and environmental stress.

“…However, the physiologic significance of these reactions is still uncertain, since some experiments suggest that NO' may protect against oxidative damage even when O-p is being generated (41,42).…”

Inhibition of low‐density lipoprotein oxidation by nitric oxide Potential role in atherogenesis

“…In macrophage-dependent oxidation of LDL, increased "NO production has been shown to be protective [9,10]; whereas, in systems containing LDL and superoxide, "NO exhibits prooxidant behavior. The simultaneous release of "NO and superoxide has been shown to modify LDL to an oxidized and potentially atherogenic form [11,12].…”