Conjugated dienes, formation

LDL isolation is used for measurement of its oxidizability under the influence of various factors in a model system using CuCl2 (final concentration 3.3 pM) as the initiator of lipid peroxidation. Oxidation of LDL was followed by changes in optical density at 234 nm (conjugated dienes formation assay) [37],... 

The results of the LDL protection determined with both methods correlate very well with each other. The linear regression between LDL oxidation assay by conjugated dienes formation and PCL (ACWLDL) for all wines was y = 0.2505X - 16.563, R2 = 0.9348. 

Parameters of protection A(Lag), change of the lag phase of conjugated dienes formation, A(ACWldl), change of the ACW of LDL after its preincubation with wine, both expressed in percentage of the initial value. 

Unconjugated dienes form the 1,3-diene complexes after isomerization to conjugated dienes. Formation of the stable conjugated diene complexe is the driving force of the isomerization. For example, the 1,4-diene in the synthetic intermediate 29 of prostaglandin A can be protected as the diene complex 30 after isomerization to the conjugated diene when it is treated with Fe2(CO)9. This method was applied to the synthesis of prostaglandin C (13). The diene complex 30 is stable for the oxidation of the lactol and introduction of the a-chain [7]. 

Initiation of lipid peroxidation and conjugated diene formation... 

Polysaccharides that are mainly found in the gel are also a group of compounds that exhibit antioxidant activities. It was demonstrated that APS-1 (mainly composed b mannose glucose in ratio 18 5) was effective in scavenging superoxide anion radical (dose-dependant fashion), hydroxyl radical, suppressed conjugated diene formation from LDL oxidation induced by Cu, and exhibited a protective effect on hydrogen peroxide-induced injury in PC12 cells 64). Also Kardosova et al. (65) showed that in vitro experiments with acidic and neutral polysaccharides were able to prevent lipid peroxidation by scavenging hydroxyl radicals. 

The rate of oxygen uptake, —d 02 /dt, is therefore directly related to the rate of conjugated diene formation, —d[CD /dt, corrected for product decomposition by the proportionality constant, K, which was found to equal 1.19, in other words 19% of the conjugated dienes decompose, so the absorbance of products has to be corrected to that... 

Conjugated diene formation can be measured by following the changes in absorbance at 234 nm [87], the wavelength maximum at which these dienes absorb. Hydroperoxide formation can be directly determined by HPLC [88 89] or indirectly by the thiocyanate method, in which hydroperoxides react with FeCl2 and thiocyanate to give a red colour which can be measured at 500 nm [90]. 

Many authors have concluded that the conjugated diene method might be used as an index of stability of lipids in place of, or in addition to PV. It is faster than iodometric PV determination, much simpler, does not depend on chemical reactions or color development, and requires a smaller sample size. However, the presence of compounds absorbing in the region of the conjugated diene formation may interfere with such determinations. It has been proposed that interference in complex systems can be minimized or eliminated by derivative spectroscopy, using photodiode detection of spectra and computer analysis of the data. ... 

The anchovy oil was stripped of tocopherols by chromatography. The relative antioxidant activity was based on inhibition of hydroperoxides measured by conjugated diene formation. 

The soybean oil was stripped of tocopherols by short-path molecular distillation. The relative potency was based on inhibition of hydroperoxides measured by conjugated diene formation at optimal concentrations of about 100 ppm for a-tocopherol, about 300 ppm for y-tocopherol. The optimal concentration for 5-tocopherol was not clearly defined and the antioxidant activity increased with concentration up to -1900 ppm. 

From Krings and Berger (2001). EthanoUc extracts tested at 20% for inhibition of conjugated diene formation on stripped maize oil free of tocopherols. 

When the cationic i7 -allylpalladiuin(II) complex is formed in the absence of nucleophiles, elimination of proton and conjugate diene formation ensues (see Sect V.2.5.1 for a specific coverage of eliminations). Formally this is a dehydration of allylic alcohols in neutral medium by prior conversion into allylic carbonate however, in some cases a tertiary base is added to accelerate proton elimination. Tsuji s group has reported the elimination in steroidal and related compounds. Different configurations at C-3 (A ring) afford different diene systems (Scheme 50). The combination of Pd(0Ac)2 and tributylphosphine is the precatalytic combination preferred by this group, which uses NMR to control the quality of the catalytic mixture. ... 

Two bioassays were used to evaluate the potency of Sal B and SM-EW-1 fraction to inhibit human LDL oxidation in vitro. The first assay was based on inhibition of malondialdehyde (MDA) formation, determined as TBARS by reacting with thiobaibituric acid (TBA), at fixed tin (2-6 hr). The ICso values indicated that Sal B (1.1 pM) was 4.0 times more potent than probucol (4.5 pM). The time course study of Sal B to inhibit conjugated diene formation in a standard LDL oxidation assay (LDL at 50 pg/mL was reacted with 5 pM Cu was also carried out in a microtiter plate (quartz) (44,45). Sal B prolonged the lag phase (ATiag) of LDL oxidation 7.5 times longer than probucol both at 1.0 pM (Table 1) (Figure 4). Sal B accounted for up to 75% of antioxidant activity in SM-EW-1 fraction. 

NOTES Oxidation of LDL (50 pg/mL) was induced by Cu (5.0 pM) at 25 C. Conjugated diene formation was monitored continuously by the increase of absorption at 234 mn. The potency of m antioxidant is defined as its c bility to prolong the lag phase. The relative potency of probucol was set as 1.00. Results are mean values of three determinations. 

Although canola oil contains a high level of OA, it also contains a relatively high level of LNA and thus the potential to increase oxidative stress in vivo. Oxidized LDL (ox-LDL) plays a fundamental role in the development of atherosclerosis. High PUFA intakes were found to promote the formation of ox-LDL whereas LPT, enriched with OA were stabler to oxidation. In vitro-conjugated diene formation (a measure of lipid oxidation) of the LDL fraction of snbjects fed diets, where canola oil or high... 

Unlike in bulk oils (Thiyam et al., 2006b), all the extracts were effective in inhibition of hydroperoxides formation compared to sinapic acid. Thus, unlike in bulk oils, the bound fractions were more effective than the unfractionated 70% methanolic extract and sinapine in the emulsified system. Furthermore, bound fractions were effective in a similar pattern as sinapic acid contrasting its activity in bulk oils. The free fraction of rapeseed extract was slightly more effective than sinapic acid in inhibiting the hydroperoxides. This corresponded to nearly the same activity in bulk oils. The results for hydroperoxides and conjugated dienes formation were in agreement. 

Human sera were obtained from healthy adult donors after overnight fasting. LDL was isolated by ultracentrifugation with the density adjusted by NaBr (p 1.006-1.063). LDL fraction was dialyzed with PBS at 4 C in darkness for 24 hr. LDL oxidation was induced by Cu (10 pM). LDL oxidation, determined by conjugated diene formation, was monitored by the increase of UV absorption at 234 nm (24,25). Antioxidant activity was determined by the capability to inhibit conjugated diene formation and prolong the lag phase (T, g, min). A concentration dependent curve was obtained for the determination of IC o value. Probucol and trolox were used as positive controls. 

---