Formation Of Reactive Products Research Articles

Influence of Phenols on the Oxidation Stability of Home Heating Oils/FAME Blends

The formation of deposits in fossil and biogenic home heating oils as well as in their blends is well-known. As a result, sediments can plug filters and nozzles in heating systems and thus cause operability problems. Different kinds of compounds are presumed to be involved in these processes. It is well-known that phenols play an important part but, on the other hand, phenols are also known to act as antioxidants that delay the oxidation of fuel compounds, and thus the formation of reactive products. To study the antioxidant effect of different phenols, model fuels (biogenic, fossil and a 10% v/v blend) were doped with several representatives of this class of compounds. The samples were artificially aged using the PetroOXY (DIN EN 16091) method. The induction time was recorded and gave information on the impact of the tested substance on the model fuel. Infrared spectrometry was used to investigate the oxidation products. Furthermore, the phenols of a commercial heating oil were extracted and then the oil...

Characterization of Ascorbylated Proteins by Immunochemical Methods

l-Ascorbic acid (AA) binds covalently to proteins in a Maillard-type reaction (protein ascorbylation). An immunochemical screening method was developed to determine the products formed during protein ascorbylation. Thus, sheep serum albumin (SSA) was incubated with l-dehydroascorbic acid (DHA) to get highly modified ascorbylated SSA (DHA−SSA), and a polyclonal anti-DHA−protein antiserum was prepared using DHA−SSA as antigen. Noncompetitive and competitive ELISAs were performed to characterize the reactive epitopes. It was found that (1) the antibody binds to ascorbylated lysine but not to arginine or histidine residues; (2) the formation of reactive products is highly dependent on the presence of oxygen; (3) proteins that were glycated by sugars, such as glucose or ribose, show significant binding to the anti-DHA−protein antibody, indicating that the reactive epitope can also be generated by carbohydrates other than AA; (4) CML-protein [CML = Nε-(carboxymethyl)lysine] and CML can inhibit the antibody binding completely. These results show that the anti-DHA−protein antiserum consists mainly of anti-CML antibodies. Using specific anti-CML and anti-oxalic acid monoamide (OMA) antibodies (Pischetsrieder, M.; Larisch, B.; Seidel, W. J. Agric. Food Chem. 1997, 45, 2070−2075), it was found that both antisera bind significantly to DHA−proteins. Therefore, it can be concluded that CML is an important product formed during the reation of AA and proteins and that it is the main immunological epitope of ascorbylated protein. However, other predominant modifications on ascorbylated proteins besides CML and OMA cannot be excluded. Keywords: l-Ascorbic acid; protein ascorbylation; immunochemical method; Maillard reaction; Nε-(carboxymethyl)lysine

Lipid peroxidation products and antioxidant enzymes in red blood cells during normal and diabetic pregnancy

Oxygen free radicals produced during normal aerobic metabolism have been implicated in several pathophysiological mammalian processes. The importance of free radical-mediated fatty acid oxidation has received much attention. The generation of active oxygen species may lead to lipid peroxidation and formation of reactive products, which may be involved in severe damage of cell molecules and structures. Free radical metabolism in pregnancy and in diabetes mellitus is still unclear. To add new insights to the question, changes in lipid peroxidation products and activities of three antioxidant enzymes: catalase (CAT), glutathione peroxidase (GPX) and superoxide dismutase (SOD) in maternal red blood cells haemolysates were evaluated in pregnant women with insulin-dependent diabetes mellitus (IDDMPW) and in healthy pregnant women (HPW). Healthy non-pregnant women were the control group for IDDM-PW and HPW, respectively. Pregnancy provoked an increase of lipoperoxidation products and an high SOD activity since early pregnancy, while CAT and GPX activities did not change during gestation. IDDM-PW showed higher content of lipoperoxidation breakdown products and lower SOD activity at each trimester, if compared with HPW; moreover, a slight increase of CAT and SOD acvitity is reported during late diabetic pregnancy. IDDM-PW were in very good metabolic control at time of sampling. The variations reported suggest an easier membrane lipoperoxidability and, consequently, an easier membrane damage during diabetic gestation.

Peroxidase-catalyzed-3-(glutathion- S-yl)- p, p′-biphenol formation

Oxidation of p, p′-biphenol with horseradish peroxidase (HRP)-hydrogen peroxide in the presence of bovine serum albumin or with bone marrow cell homogenate-hydrogen peroxide resulted in the formation of reactive products that conjugate with protein. Glutathione prevented the protein binding. Glutathione readily reacted with p, p′-biphenoquinone, the principal oxidation product of p, p′-biphenol in the HRP-hydrogen peroxide system and resulted in the formation of several glutathione conjugates, p, p′-biphenol and small amounts of oxidized glutathione. The major glutathione conjugate was identified as 3-(glutathion- S-yl)- p, p′-biphenol by high field nuclear magnetic resonance and fast atom bombardment mass spectrometry. The same conjugate was formed in the bone marrow homogenate-hydrogen peroxide system. p, p′-Biphenoquinone reduction by glutathione to p, p′-biphenol without glutathione oxidation was explained by the rapid reduction of p, p′-biphenoquinone by 3-(glutathion- S-yl)- p, p′-biphenol.

General aspects on biotransformation and elimination of organic compounds in connection with occupational exposure.

A general review of the common pathways for biotransformation (metabolism) of foreign organic compounds, i.e. xenobiotics, is presented. Many factors are mentioned that can influence the result of exposure to chemicals and thus the toxicity: Firstly the uptake is often influenced by some factors, e.g. by the work load. Secondly, the type of and capacity for biotransformation is influenced by e.g. genetic background and can be increased by induction of capacity limiting enzymes and decreased by e.g. inhibition. Interferences with other chemicals, drugs and alcohol can cause significant adverse effects. Potential risks that may be linked with biotransformation are discussed, as for example the formation of reactive products, e.g. epoxides which may initiate cancer and allergy. Thirdly, the rate of elimination is influenced by e.g. depots, degree of protein binding, and liver as well as kidney function. Many arguments are presented for analysis of substances or biotransformation products and the use of biochemical limit values. In short, this implies a health control of each individual and his characteristic response.