Lipid hydroperoxides aldehydes

Separation of reaction products HPLC or GC analysis of aldehydes, lipid hydroperoxides, cholesterol esters, and phospholipids. 

Oxidative stress Lipid oxidation Oxygen absorption Manometric, polarographic Diene conjugation HPLC, spectrophotometry (234 nm) Lipid hydroperoxides HPLC, GC-MS, chemiluminescence, spectrophotometry Iodine liberation Titration Thiocyanate Spectrophotometry (500 nm) Hydrocarbons GC Cytotoxic aldehydes LPO-586, HPLC, GC, GC-MS Hexanal and related end products Sensory, physicochemical, Cu(II) induction method, GC TBARS Spectrophotometry (532-535 nm), HPLC Rancimat Conductivity F2-iP GC/MS, HPLC/MS, immunoassays... 

A correlation may be established between the concentration of oxidized lipids and the TEARS value, expressed as MDA equivalents, in uM units. Correction is due in some cases for the interference by dyes or other factors. For example, the presence of anthocyanins in red cabbage leaves or turbiditjf causes overestimation of lipid hydroperoxides in plant tissue by the TEARS method. TEARS was used to assert the level of endogenous peroxides in hypo- and hyperthyroidism, both conditions being characterized by low lipid and lipoprotein plasma levels and enhanced oxidative metabolism . In a procedure for determination of TEARS in edible oils, the sample is placed in a centrifuge at 12000 g before measuring at 532 nm (e = 1.56 x 10 M cm ) . A usual procedure for determination of TEARS in certain complex matrices involves steam distillation of the aldehydes responsible for the value, instead of extraction. In nitrite-cured meats, excess nitrite may cause nitrosation of MDA, thus interfering with distillation. To avoid this interference sulfanilamide is added, which is converted to a diazonium salt and... 

Yamamoto K, Kawanishi S (1989) Hydroxyl free radical is not the main active species in site- specific DNA damage induced by copper(ll) ion and hydrogen peroxide. J Biol Chem 264 15435-15440 Yang M-H, Schaich KM (1996) Factors affecting DNA damage caused by lipid hydroperoxides and aldehydes. Free Rad Biol Med 20 225-236... 

Lipid peroxidation (Figure 14.5) is the initiating reaction in a cascade of events, starting with the oxidation of unsaturated fatty acids to form lipid hydroperoxides, which then break down to yield a variety of end products, mainly aldehydes, which can go on to produce toxicity in distal tissues. For this reason cellular damage results not only from the breakdown of membranes such as those of the endoplasmic reticulum, mitochondria, and lysosomes but also from the production of reactive aldehydes that can travel to other tissues. It is now thought that many types of tissue injury, including inflammation, may involve lipid peroxidation. 

Whilst these observations point to a potentially important cell-regulatory role for HNE, little is known about factors that control the rate of its production. Clearly a prerequisite is the formation of cellular lipid hydroperoxides, but although levels of those can apparently be modulated by serum factors there is a need to explore mechanisms, possibly enzymatic, whereby HNE levels might be tightly regulated. In this context it is known that HNE can serve as a substrate for glutathione transferase [64], or aldehyde dehydrogenase [66] ... 

Proteins adjacent to peroxidizing phospholipids may undergo modification by the interaction of the free amino groups of the side-chains of the substituent lysine residues with a range of aldehydic metabolites of lipid hydroperoxide breakdown. 

As oxidation normally proceeds very slowly at the initial stage, the time to reach a sudden increase in oxidation rate is referred to as the induction period (6). Lipid hydroperoxides have been identified as primary products of autoxidation decomposition of hydroperoxides yields aldehydes, ketones, alcohols, hydrocarbons, volatile organic acids, and epoxy compounds, known as secondary oxidation products. These compounds, together with free radicals, constitute the bases for measurement of oxidative deterioration of food lipids. This chapter aims to explore current methods for measuring lipid oxidation in food lipids. 

Oxidation of LDL can be divided into different stages i) initiation of lipid peroxidation ii) propagation of PUFA-mediated lipid peroxidation iii) decomposition of lipid hydroperoxides into reactive aldehydes and ketones, and iv) modification of apo B, leading to recognition of LDL by the macrophage scavenger receptor. 

Free radical chain reactions, which occur during lipid peroxidation, lead to formation of lipid hydroperoxides that decompose to several types of secondary free radicals and a large number of secondary reactive compounds, such as aldehydes, all resulting in the destruction of cellular membranes and other cytotoxic responses. 

Thus, the events form the basis of a chain-reaction process. The lipid hydroperoxide decomposition produces more radicals and noxious aldehydes... 

Analysis of the Decomposition Products of Hydroperoxides. Some authors have monitored formation of some of the decomposition products of the lipid hydroperoxides. Direct spectrophotometric measurements of the formation of oxo-octadecadienoic acids at 280 nm are possible , as are measurements of secondary oxidation products like a-diketones and unsaturated ketones at 268 nm. The formation of various aldehyde products of lipid peroxide decomposition can be monitored by reacting them with 2,4-dinitrophenylhydrazine and, after HPLC separation, measuring at 360-380 mn the DNPH derivatives formed , althongh the sensitivity of this particular technique makes it very susceptible to interference. 

Figure 6 Short-chain aldehydic products resulting from the oxidative fragmentation of lipid hydroperoxides.

Polyunsaturated fatty acids and especially arachidonic acid are highly susceptible to lipid peroxidation, which leads to the generation of lipid hydroperoxides, which then undergo carbon-carbon bond cleavage giving rise to the formation of short chain, unesterified aldehydes and aldehydes still esterified to the parent lipid, termed core-aldehydes (Esterbauer et al. 1987). Considerable progress has been made in recent years in dissecting the molecular structures of OxPL, which consequently allowed for the experimental use of defined compounds rather than complex lipoproteins and lipid mixtures. 

Malondialdehyde (MDA) and 4-hydroxy-2-nonenal (HNE) are among many reactive aldehydes that are nonenzymatic lipid peroxidation products. These products are illustrated in Fig. 5. Both have been intensively studied as an index of peroxidation (E4). They are not only associated with arteriosclerosis (J9), but are among those electrophilic aldehydes that adduct lysine residues in apo B, leading to uncontrolled OxLDL uptake by macrophages (Ul). Moreover, both react with lipid hydroperoxides and decompose them to peroxyl and alkoxyl radicals, which can reinitiate lipid peroxidation (E4, J4, R5, Ul, W9). 

---