The reaction of malonaldehyde with wheat flour proteins

Malondialdehyde measurement in urine

Malondialdehyde (MDA) is an end product of lipid peroxidation and is a frequently measured index of these processes. The thiobarbituric acid (TBA) test is commonly used to measured MDA, but its specificity is questionable due to the presence of interfering chromogens. Wade and van Rij described in 1988 a method which removes these chromogens by HPLC. However, the sensitivity and the resolution of this method was not adequate for measurements of MDA in urine. We have improved this method by replacing TBA with diethylthiobarbituric acid (DETBA). The less polar MDA-DETBA complexes were isolated on Bakerbond cartridges and quantified by HPLC without interference. MDA was detectable using a fluorescence or ultraviolet detector at picomole levels. This technique was applied to urine samples obtained from ten burns patients on different days following their hospitalization. Urinary MDA in burns patients was very high and reached 18.6 mumol/mmol creatinine in one patient compared with a mean value of 0.23 mumol/mmol creatinine in healthy controls. Maximum MDA levels were attained on the third day for the majority of patients and remained, on average, much higher than normal even after 20 days. Using this method, picomole quantities of MDA can be easily and specifically detected in urine samples. This method is useful for assessing an oxidative stress.

[Interaction of lipids and meat proteins. 2. Digestibility of proteins in vitro, thermohydrolysis of collagen, changes in the content of essential amino acids and coefficients of the relative nutritive value of proteins]

Changes in the nutritive value of meat under the influence of an interaction between oxidized fats and proteins were studied in model experiments. Parameters were the digestibility of protein, sensitivity of tissue against thermohydrolysis, changes in the content of essential amino acids and in the RNV coefficient of the protein. Muscle gel and tissue served as meat substrates, methyl ester of linoleic acid and its oxidation products were used as fat substrates. It has been found that reactions of the oxidation products of methyl linoleate with meat proteins lead to a crosslinking of proteins. Hexanal and hydroperoxide of the oxidized methyl linoleate influence the decrease in digestibility of muscle protein and the thermohydrolysis of the collagen. Proteins of pasteurized gels showed losses in essential amino acids, which corresponded to a lower nutritive value (determined in the RNV coefficient).

Measurement of free and bound malondialdehyde in vitamin E-deficient and -supplemented rat liver tissues

The quantity of free malondialdehyde (MDA) in liver tissues of rats fed vitamin E-deficient or -supplemented diets for 43 wk was measured by a newly developed high performance liquid chromatographic (HPLC) method. Bound MDA was quantified by the same HPLC method after alkaline hydrolysis of tissue homogenates. Tissues from vitamin E-deficient animals showed levels of free MDA about 15 times higher but levels of bound MDA less than 2 times higher than the vitamin E-supplemented animals. Free MDA is the major form in vitamin E-deficient tissues, but bound MDA is predominant in vitamin E-supplemented tissues. Conventional thiobarbituric acid (TBA) test results revealed that the content of TBA-reactive substances expressed in MDA equivalents was much higher than the actual free MDA levels in all groups. Results indicate that free MDA level measured by HPLC is a more sensitive index than the TBA value for lipid peroxidation. Some other TBA-reactive substances seem to exist in liver tissue regardless of the dietary treatment.

The effects of high ethanol doses on rates of ethanol oxidation in rats. A reassessment of factors controlling rates of ethanol oxidation in vivo

1. Ethanol was oxidised more slowly by rats which were given an ethanol dose of 5.1 g/kg than by rats which were given an ethanol dose of 1.4 g/kg. 2. A positive correlation was found between [lactate]/[pyruvate] ratios and rates of ethanol oxidation. 3. Acetaldehyde concentrations varied widely between rats, but in some cases were high enough to influence rates of ethanol oxidation. 4. Liver alcohol dehydrogenase levels were just sufficient to account for ethanol oxidation rates observed in vivo. 5. Pre-administration of a large ethanol dose (6.5 g/kg) did not alter mean [lactate]/[pyruvate] ratios or ethanol oxidation rates during metabolism of test doses of 2.5 g/kg. 6. Injection of pyruvate did not increase rates of ethanol oxidation. 7. The results do not support suggestions that a high-Km ethanol oxidising system plays an important role in vivo, that increased rates of ethanol oxidation can be induced by large, acute ethanol doses or that the rate of NADH reoxidation controls rates of ethanol metabolism. 8. The results support other evidence which has indicated that the level of alcohol dehydrogenase is the major factor limiting rates of ethanol oxidation in vivo.

[Effect of natural amino acids on ethanol oxidation in isolated rat hepatocytes]

The effects of the various naturally occurring amino acids on ethanol oxidation in hepatocytes from starved rats was systematically studied. In order to minimize the non ADH pathways, the ethanol concentration used was 4 mmol/litre, the amino acids being added at the same concentration. In hepatocytes from fasted rats, alanine, arginine, asparagine, aspartate, citrulline, cysteine, glutamate, glutamine, glycine, histidine, hydroxyproline, ornithine and serine increase significantly ethanol consumption. The stimulatory effect of glutamine being much less pronounced than the asparagine one and proline being devoid of action, the influence of ammonium chloride addition on ethanol consumption in the presence of these amino acids was studied. Ammonium chloride determines an enhancement of ethanol oxidation in these conditions, the results showing no apparent correlation between intracellular glutamate concentration and ethanol oxidation rate, contrarily to previous data. In hepatocytes from fed rats, only alanine, asparagine, cysteine, glycine, hydroxyproline, ornithine and serine increase ethanol oxidation, although to a lesser extent than in cells from starved rats.