Beta-ethoxyacrolein contamination increases malondialdehyde inhibition of milk xanthine oxidase activity

Behavior of Malondialdehyde in Oil-in-Water Emulsions

The impact of temperature, emulsifier, and protein type on the reactivity of malondialdehyde in oil-in-water emulsions was elucidated. Malondialdehyde recoveries in aqueous buffer, protein solutions, saturated oil, and fully hydrogenated coconut oil-in-water emulsions stabilized by whey proteins or Tween 20 at 4 or 40 °C were compared. At both temperatures, the reactivity of malondialdehyde in aqueous buffer was the same. In protein solutions, malondialdehyde concentrations were reduced further and its decrease was protein-dependent. Similar trends were found for emulsions. Surprisingly, malondialdehyde was very reactive in saturated oil because only 15% was recovered at 40 °C. However, the degradation in oil proved to be strongly temperature-dependent; at 4 °C, losses amounted to only 8%. This study revealed that malondialdehyde is a very reactive molecule, both in the presence and absence of proteins. Its use as a general oxidation marker should therefore be considered with care.

Biochemical measurement of neonatal hypoxia

Neonatal hypoxia ischemia is characterized by inadequate blood perfusion of a tissue or a systemic lack of oxygen. This condition is thought to cause/exacerbate well documented neonatal disorders including neurological impairment. Decreased adenosine triphosphate production occurs due to a lack of oxidative phosphorylation. To compensate for this energy deprived state molecules containing high energy phosphate bonds are degraded. This leads to increased levels of adenosine which is subsequently degraded to inosine, hypoxanthine, xanthine, and finally to uric acid. The final two steps in this degradation process are performed by xanthine oxidoreductase. This enzyme exists in the form of xanthine dehydrogenase under normoxic conditions but is converted to xanthine oxidase (XO) under hypoxia-reperfusion circumstances. Unlike xanthine dehydrogenase, XO generates hydrogen peroxide as a byproduct of purine degradation. This hydrogen peroxide in combination with other reactive oxygen species (ROS) produced during hypoxia, oxidizes uric acid to form allantoin and reacts with lipid membranes to generate malondialdehyde (MDA). Most mammals, humans exempted, possess the enzyme uricase, which converts uric acid to allantoin. In humans, however, allantoin can only be formed by ROS-mediated oxidation of uric acid. Because of this, allantoin is considered to be a marker of oxidative stress in humans, but not in the mammals that have uricase. We describe methods employing high pressure liquid chromatography (HPLC) and gas chromatography mass spectrometry (GCMS) to measure biochemical markers of neonatal hypoxia ischemia. Human blood is used for most tests. Animal blood may also be used while recognizing the potential for uricase-generated allantoin. Purine metabolites were linked to hypoxia as early as 1963 and the reliability of hypoxanthine, xanthine, and uric acid as biochemical indicators of neonatal hypoxia was validated by several investigators. The HPLC method used for the quantification of purine compounds is fast, reliable, and reproducible. The GC/MS method used for the quantification of allantoin, a relatively new marker of oxidative stress, was adapted from Gruber et al. This method avoids certain artifacts and requires low volumes of sample. Methods used for synthesis of MMDA were described elsewhere. GC/MS based quantification of MDA was adapted from Paroni et al. and Cighetti et al. Xanthine oxidase activity was measured by HPLC by quantifying the conversion of pterin to isoxanthopterin. This approach proved to be sufficiently sensitive and reproducible.

Glucose-stimulated acrolein production from unsaturated fatty acids

Glucose auto-oxidation may be a significant source of reactive oxygen species (ROS), and also be important in the lipid peroxidation process, accompanied by the release of toxic reactive products. We wanted to demonstrate that acrolein can be formed directly and actively from free fatty acids in a hyperglycemic environment. A suspension of linoleic and arachidonic acids (2.5 mM) was exposed to different glucose concentrations (5, 10 and 15 mmol/L) in vitro. The samples were extracted with organic solvents, partitioned, followed at 255-267 nm, and analysed using capillary electrophoresis and mass spectroscopy. The total release of aldehydes significantly (P < 0.01) increased from 1.0 to 5.1, 8.3 and 13.1 micromol/L after 6 hours of incubation, proportional to glucose concentrations. It was possible to verify a correlate hydroperoxide formation as well. Among the lipid peroxidation products, acrolein (5% of total) and its condensing product, 4-hydroxy-hexenal, were identified. From the results presented here, it was possible to demonstrate the production of acrolein, probably as a fatty acid product, due to free radicals generated from the glucose auto-oxidation process. The results led us to propose that acrolein, which is one of the most toxic aldehydes, is produced during hyperglycemic states, and may lead to tissue injury, as one of the initial problems to be linked to high levels of glucose in vivo.

Validation of methyl malondialdehyde as internal standard for malondialdehyde detection by capillary electrophoresis

The aim of this study was to validate, by capillary electrophoresis, the use of synthesized methyl malondialdehyde as the internal standard for the direct quantification of free and total (free+bound) malondialdehyde in biological samples. All analyses were performed in 20 cm x 50 microm uncoated capillaries at 20 degrees C, using 25 mmol/L borax (pH 9.3) and 5 mmol/L tetradecyltrimethylammonium bromide as running buffer. The applied voltage was -4kV (about 8 microA), the detector being set at 260 nm for a total run time of 8 min per sample. Free malondialdehyde was evaluated after acetonitrile extraction, while the samples evaluated for total malondialdehyde were, before extraction, hydrolyzed for 1h at 60 degrees C in the presence of 1 mol/L NaOH. The detection threshold was 0.2 micromol/L in microsomes and 0.4 micromol/L in plasma. As an application of the method, three pools of rat liver microsomes were quantified before (0.35+/-0.1 and 1.1+/-0.5 nmol/mg protein, free and total malondialdehyde, respectively, mean+/-SD) and after lipoperoxidation induction using systems able to generate oxygen free radicals (18.4+/-3.2 and 19.7+/-2.0 nmol/mg protein). The results were confirmed by isotopic dilution gas chromatography-mass spectrometry, used as the reference method. The feasibility of capillary electrophoresis for malondialdehyde determination in normal and pathological human plasma was also investigated.

Oxidative status and malondialdehyde in beta-thalassaemia patients

BACKGROUND

In beta-thalassaemia syndromes, decreased or impaired biosynthesis of beta-globin leads to accumulation of unpaired alpha-globin chains. Moreover, the iron overload in beta-thalassaemia patients generates oxygen-free radicals and peroxidative tissue injury. The aim of this study was to detect and correlate iron overload parameters with the oxidative stress and the antioxidant capability in beta-thalassaemia patients.

DESIGN

Serum iron, transferrin saturation, serum ferritin, nontransferrin-bound iron (NTBI), levels of serum free and total (free + bound) malondialdehyde (MDA) and total peroxyl radical-trapping antioxidant parameter (TRAP) were evaluated in 21 regularly transfused beta-thalassaemia major (TM) patients, 13 untransfused beta-thalassaemia intermedia (TI) patients and 17 healthy controls. Blood from the TM patients was drawn 48 h after the last desferoxamine (20-40 mg kg(-1)) infusion and just before transfusion.

RESULTS

Free and total MDA and NTBI levels were higher in the TM patients than in the TI. In the TM patients the free MDA levels correlated positively with serum iron (r = +0.3, P = 0.0006), whereas the total MDA correlated positively with NTBI (r = +0.45, P = 0.037). However, a negative correlation was observed between TRAP and NTBI (r = -0.4, P = 0.0006). In the TI patients there was no significant correlation between free or total MDA and TRAP or NTBI.

CONCLUSIONS

Our results confirm the peroxidative status generated by iron overload in thalassaemia patients and highlight the rapid formation of marked amounts of free MDA despite the chelation therapy in TM patients.

Mechanisms of action of malondialdehyde and 4-hydroxynonenal on xanthine oxidoreductase

Studies have been made on the possible involvement of malondialdehyde (MDA) and (E)-4-hydroxynon-2-enal (HNE), two terminal compounds of lipid peroxidation, in modifying xanthine oxidoreductase activity through interaction with the oxidase (XO) and/or dehydrogenase (XDH) forms. The effect of the two aldehydes on XO (reversible, XO(rev), and irreversible, XO(irr)) and XDH was studied using xanthine oxidase from milk and xanthine oxidoreductase partially purified from rat liver. The incubation of milk xanthine oxidase with these aldehydes resulted in the inactivation of the enzyme following pseudo-first-order kinetics: enzyme activity was completely abolished by MDA (0.5-4 mM), while residual activity (5% of the starting value) associated with an XO(irr) form was always observed when the enzyme was incubated in the presence of HNE (0.5-4 mM). The addition of glutathione to the incubation mixtures prevented enzyme inactivation by HNE. The study on the xanthine oxidoreductase partially purified from rat liver showed that MDA decreases the total enzyme activity, acting only with the XO forms. On the contrary HNE leaves the same level of total activity but causes the conversion of XDH into an XO(irr) form.

Oxidative Stress and Homocysteine in Coronary Artery Disease

Background: Oxidative stress is present in cardiovascular diseases (CVDs), and hyperhomocysteinemia, an independent risk factor for these diseases, may play a role by inducing production of oxygen free radicals.

Methods: To evaluate the possible role of homocysteine (Hcy) in inducing oxidative stress in coronary artery disease (CAD), plasma Hcy was measured in 68 consecutive cardiovascular patients, and plasma malondialdehyde (MDA), both free and total (free + bound), was measured in 40 patients with CAD (18 with chronic stable angina and 22 with unstable angina). As controls, we tested 70 healthy volunteers. Hcy was measured by an immunoenzymatic method and MDA, an index of lipid peroxidation, by gas chromatography–mass spectrometry.

Results: Plasma Hcy concentrations were significantly higher in cardiovascular patients than in controls (10.2 vs 8.9 μmol/L; P &lt;0.0002), with no significant difference between values in the stable and unstable angina subgroups. Similarly, total MDA was significantly higher in the CAD group than in the controls (2.6 vs 1.3 μmol/L; P &lt;0.00001), again with no significant difference between stable and unstable angina patients. By contrast, free MDA, which was significantly higher in the CAD patients than the controls (0.4 vs 0.2 μmol/L; P &lt;0.00001), was also significantly higher in the unstable than in the stable angina group (0.5 vs 0.3 μmol/L; P &lt;0.03). However, no correlation was observed among Hcy and free and total MDA.

Conclusions: Our findings show that a moderate increase of Hcy is associated with CVD but that Hcy at the detected values cannot be considered completely responsible for oxidative damage. That lipid peroxidation is involved in CAD is shown by our observation of significantly increased plasma free and total MDA concentrations compared with controls. Moreover, free MDA values discriminated between unstable and chronic stable angina, and could thus represent a new diagnostic tool.