Showing papers on "Methylglyoxal published in 1978"

Electronic properties of some protein--methylglyoxal complexes.

Abstract: Steady-state conductivity measurements and dielectric measurements in the frequency range 10(-5) to 100 Hz are reported for samples of bovine serum albumin, casein, and lysozyme complexed with methylglyoxal. Compared with the untreated proteins, the brown complexed proteins exhibit an increased conductivity and free electron spin density, together with a low-frequency dielectric dispersion. These results can be taken as evidence that the interaction with methylglyoxal results in the proteins possessing an increased electronic activity associated with the creation of mobile electron holes within the valence band states of the protein molecules.

Concanavalin A Increases Glyoxalase Enzyme Activities in Polymorphonuclear Leukocytes and Lymphocytes

Abstract: Glyoxalase I converts methylglyoxal and glutathione to S-lactoylglutathione and glyoxalase II converts this compound to D-lactic acid, regenerating glutathione in the process. A recent study from my laboratory has provided evidence that S-lactoylglutathione modulates microtubule assembly in vitro whereas concanavalin A (Con A) has been shown to increase microtubule occurrence in polymorphonuclear leukocytes (PMN). The present report describes the dose-dependent activation by Con A of both glyoxalase I and II in PMN and lymphocytes. In nine experiments with PMN, Con A (100 microgram/ml) increased glyoxalase I and II activities by 19 +/- 8% and 12 +/- 10% (mean +/- S.D.). In 17 experiments with lymphocytes, activation of the two enzymes by 10 microgram/ml Con A was 30 +/- 14% and 28 +/- 8%. Changes occurred after a 1-min incubation with Con A and persisted for at least 60 min. Since both enzyme activities are increased it is not clear if S-lactoylglutathione levels are increased or decreased but presumably they change. The present findings are compatible with the hypothesis that Con A increases microtubule occurrence in PMN by affecting the glyoxalase enzymes. They also represent a newly described early biochemical change caused by Con A in lymphocytes.

Carcinostatic activity of methylglyoxal and related substances in tumour-bearing mice.

Abstract: Methylglyoxal treatment of tumour cells in vitro primarily depresses protein synthesis, in contrast to trans-4-hydroxypent-2-enal (HPE) which preferentially inhibits DNA synthesis. Methylglyoxal and hpe are potent carcinostatic agents in vitro but relatively ineffective in vivo. Both aldehydes have a short half-life in vivo which may explain their poor carcinostatic properties when administered other than peritumorally. Several possibilities of increasing the effective half-life were investigated including (i) multiple intraperitoneal injections, (ii) concomitant administration of an inhibitor of glyoxalase I, (iii) administration of aldehyde-cysteine adducts, and (iv continuous intravenous infusion. Methylglyoxal (36 mg/kg i.p., twice daily) was slightly less effective in inhibiting the growth of the solid form of Ehrlich carcinoma than a dose of 72 mg/kg (inj. 1); 36 mg/kg (inj. 2) 46.2% compared to 51%. The aldehyde was more effective aginst the ascitic form of the tumour, with 99.76% inhibition of growth after giving 72 mg/kg twice daily for five days followed by 36 mg/kg for five days. The glyoxalase I inhibitor S-(p-bromobenzyl)-glutathione didnot significantly enhance the activity of methylglyoxal against the solid form of the tumour. Nicotinamide (1% w/v in the drink) was similarily inactive. Methylglyoxal in combination with nicotinamide was significantly more effect (P less than 0.05) than methylglyoxal alone (36 mg/kg, twice daily) in inhibiting the growth of the ascitic tumour. Methylglyoxal-N-acetyl-L-cysteine was four times less toxic than methylglyoxalalone but was marginally less effective against the ascitic form of the tumour. Doses of these adducts equivalent to 144 mg/kg per day of methylglyoxal were more effective P less than 0.05) than the optimal regime of methylglyoxal in inhibiting the solid tumour (67.5% inhibition compared to 51%). Treatment of mice bearing the ascitic form of Sarcoma 180 with five daily doses (i.p.) of an HPE-cysteine adduct equivalent to a dose of HPE alone of 32-256 mg/kg per day significantly increased survival time by comparison with controls. The adduct was 2-3 times more effective, dose-for-dose, than HPE alone in inhibiting tumour growth. Purified buffered methylglyoxal has an LD50 on continuous infusion into the right lateral tail vein in mice of more than 3.0 mg/g per day (seven days at 2.8 ml/day). Local oedema followed by tail necrosis occurs at doses in excess of 0.25-0.5 mg/g per day in mice bearing the solid forms of the syngeneic tumours: squamous carcinoma D; lymphosarcoma 1 (WH/Ht mice); and spontaneous mammary D5056 (CBA/CA mice). A maximum tumour volume growth delay of 3.4 days at Day 17 (P less than 0.001) after transplantation was observed after infusion of 0.5 mg/g per day methylglyoxal on Days 11-17 in the CBA/CA D40 syngeneic mammary tumour. Tumour regrowth after termination of therapy eliminated the significant difference between control and methylglyoxal-treated tumours by Day 27. Methylglyoxal infusion (0...

Isolation of methylglyoxal from liver.

Abstract: Acetaldehyde and methylglyoxal were shown to be present in liver bound to protein. They were isolated in the form of 2,4-dinitrophenylhydrazones and osazones, respectively. The NMR spectrum of pure methylglyoxal was recorded.

Effects of Glyceraldehyde on the Structural and Functional Properties of Sickle Erythrocytes

Abstract: The d- and l-isomers of glyceraldehyde are equally effective in the inhibition of SS erythrocyte sickling in vitro. The following compounds at a concentration of 20 mM were ineffective in inhibiting sickling: glyceraldehyde-3-phosphate, d-erythrose, d-ribose, d-fructose, d-glucose, d-sucrose, dihydroxyacetone, and methylglyoxal. Glyceraldehyde does not reverse the sickling of cells in the deoxy state. The properties of purified hemoglobin after treatment with glyceraldehyde and of the hemoglobin isolated from treated cells are very similar; these results suggest that glyceraldehyde itself is the reactive species within the erythrocyte. Erythrocyte glutathione is decreased by treatment in vitro with the aldehyde. Relatively high concentrations of glyceraldehyde (50 mM) lead to a small amount (3%) of cross-linking between hemoglobin monomers as well as to some cross-linking of erythrocyte membrane proteins. Lower concentrations of dl-glyceraldehyde (5-20 mM), which reduce the sickling of erythrocytes in vitro, lead to proportionally less cross-linking of hemoglobin. Cells that have been treated with those concentrations of the aldehyde show little change in their osmotic fragility, exhibit improved filtration properties, and have a lowered viscosity.

Methylglyoxal production in human blood.

Abstract: The research of Szent-Gyorgyi and others has suggested that the three-carbon ketoaldehyde methylglyoxal has a potential role in the control of cell growth. Its metabolism to D-lactate (not the L-lactate of glycolysis) is catalysed by the mammalian enzymes glyoxalase I (S-lactoyl-glutathione methylglyoxal-lyase, isomerizing; EC 4.4.1.5) and glyoxalase II (S-2-hydroxyacylglutathione hydrolase; 3.1.2.6), with glutathione as a coenzyme. Direct determination of methylglyoxal in biological tissues is difficult because of the active glyoxalase system. However, the product of the glyoxalase system, D-lactate, should indicate formed or added methylglyoxal. A stereospecific assay was used to measure D-lactate in human plasma; it involved the spectrophotometric analysis of NADH at 340 nm catalysed by D-lactate dehydrogenase (D-lactate:NAD+ oxidoreductase; EC 1.1.1.28) from Lactobacillus leichmannii. Blood collected by venepuncture was used for the determination of the plasma concentration of D-lactate. The mean concentration for seven normal subjects was 0.023 mM +/- 0.002 S.E.M. When the glycolytic pathway in whole blood was inhibited in vitro with fluoride, a significant increase in D-lactate was found (about 0.15 mM/hour at 37 degrees C). Added methylglyoxal also produced an increase in D-lactate formation. Some specific precursors of L-lactate (dihydroxyacetone phosphate, for example) added to whole blood produced an increased concentration of D-lactate, even when glycolysis was not inhibited. This finding indicates that catabolites of glucose lead to methylglyoxal synthesis and suggest a control function for the glyoxalase enzyme system in glycolysis that could be exploited for cancer therapy.

Diminished excretion of polyamines from BHK-21/C13 cells exposed to methylglyoxal bis(guanylhydrazone).

Abstract: Methylglyoxal bis(guanylhydrazone) (1,1'-[methylethanediylidine)dinitrilo]diguanidine) inhibited the growth of BHK-21/C13 cells in monolayer cultures. Accumulation of spermidine and spermine was inhibited, whereas the accumulation of putrescine was increased. The intracellular spermidine/spermine molar ratio decreased conly slightly after exposure of the cells to 20 micrometer-methylglyoxal bis(guanylhydrazone) for 1 day. Cells incubated in the presence of the drug released less polyamine into the culture medium that did control cells, the polyamine released consisting almost exclusively of spermidine, both free and as a conjugated form.

Biological activity of methylglyoxal and related aldehydes.

Abstract: The effect of methylglyoxal and other aldehydes on several biochemical variables has been studied. Aldehydes inhibit amino acid incorporation into proteins, both in reconstituted systems and in isolated hepatocytes. They also decrease the secretion of protein and lipoprotein from hepatocytes into the incubation medium. This inhibition is seen even with prelabelled proteins, which indicates damage to the secretory mechanism itself. This conclusion is strenghened by the fact that aldehydes also decrease the binding of colchicine to liver tubulin. Aldehydes decrease the respiratory rate of mitochondria, as well as mitochondrial swelling induced by phosphate, by Ca2+ or by K+ plus valinomycin. They also partially inhibit cytochrome P-450. When injected into normal rats, aldehydes produce a decrease in the mitotic index of bone marrow cells and of the epithelial lining of the small intestine. A decrease in mitotic index and in cellularity is seen after injecting aldehydes into the peritoneal cavity of rats bearing transplanted ascites AH-130 Yoshida hepatoma. Aldehydes also impair the function of liver cell ligandin and potentiate the increase in cell permeability induced by 5-hydroxytryptamine (serotonin). The meaning of these results is discussed with special reference to the pathogenesis of cellular lesions in carbon tetrachloride poisoning.

Electronic and dielectric properties of protein--methylglyoxal complexes.

Abstract: Steady-state conduction and dielectric measurements over the frequency range 10(-5) to 10(5) Hz are reported for several proteins that have been complexed with methylglyoxal. Compared with the normal (white) proteins the brown protein--methylglyoxal complexes exhibit a marked increase in electronic conductivity and a pronounced low-frequency dielectric dispersion. The intensity of the brown colour and the electronic activity is directly related to the number of free lysine groups available to react with the methylglyoxal. It is proposed that the methylglyoxal molecules form Schiff bases with the epsilon-amino groups of lysine residues and that these Schiff bases then form a charge-transfer complex with a neighbouring peptide unit. For collagen, in particular, it is found that the electron 'holes' so formed in the polypeptide backbone are capable of long range motion in what can be interpreted as being the valence band of extended electronic states of the protein structure. The protein--methylglyoxal complexes have electronic and dielectric properties similar to those exhibited by the perylene-chloranil charge-transfer complex.

The Search for New Cancerostatic Agents

Abstract: Following the lead given by Albert Szent-Gyorgyi's bioelectronic theory of cancer, work was continued in two major directions: (i) designing new electrophilic molecules, related to methylglyoxal, and (ii) using L-ascorbic acid as a (non-toxic) carrier for methylglyoxal and its derivatives in the form of its acetals. The vinylogue of methylglyoxal, 4-oxopent-2-enal, was expected to be a most reactive electron acceptor, on the basis of quantum mechanical calculations by J.J. Ladik's group. A new reaction, the formation of the ene-2, 3-diol acetal and hemiacetal-hemiketal, was found to occur with 'conjugated' aldehydes, such as methylglyoxal, glyoxal, phenylglyoxal, malealdehyde and acrylaldehyde; the reaction proceeded very smoothly with 4-oxopent-2-enal. The structural determination of these new types of acetals by 1H and 13C n.m.r. spectroscopy and by chemical methods is discussed.

Interactions of methylglyoxal with methylamine.

Abstract: Ab initio quantum mechanical calculations are used to study the interactions of the aldehydic group of methylglyoxal with the NH2 groups of protein side-chains, using methylamine as a representative molecule. The hydrogen-bonding interaction, C = O...H - N, results in an electronic charge transfer from methylglyoxal to methylamine in both the ground and first excited triplet states. In this latter state a slight possibility is found for the H atom in the hydrogen bond to tunnel from methylglyoxal to methylamine, leading to the possible formation of two free radical fragments. The approach of methylamine to methylglyoxal in the stacked conformation C...N to form a hemiacetal, associated with electron charge transfer from methylamine to methylglyoxal, is energetically unfavourable in vacuum. The concomitant tunnelling of a proton from a proton-donating solvent molecule to the aldehydic oxygen of methylglyoxal is shown to make this approach favourable. The relative stability of the keto and enol forms of methylglyoxal is also investigated, the keto form being found the more stable in vacuum.