The reversal of phenylarsenoxide inhibition of keto acid oxidation in mitochondrial and bacterial suspensions by lipoic acid and other disulphides

Thioredoxin and dihydrolipoic acid are required for 3-mercaptopyruvate sulfurtransferase to produce hydrogen sulfide

H2S (hydrogen sulfide) has recently been recognized as a signalling molecule as well as a cytoprotectant. We recently demonstrated that 3MST (3-mercaptopyruvate sulfurtransferase) produces H2S from 3MP (3-mercaptopyruvate). Although a reducing substance is required for an intermediate persulfide at the active site of 3MST to release H2S, the substance has not been identified. In the present study we show that Trx (thioredoxin) and DHLA (dihydrolipoic acid) associate with 3MST to release H2S. Other reducing substances, such as NADPH, NADH, GSH, cysteine and CoA, did not have any effect on the reaction. We also show that 3MST produces H2S from thiosulfate. The present study provides a new insight into a mechanism for the production of H2S by 3MST.

Alpha lipoic acid (ALA) protects proteins against the hydroxyl free radical-induced alterations: rationale for its geriatric topical application

The well known OH* free radical scavenging properties of alpha-lipoic acid (ALA) cannot be easily utilized for biological experiments, because the compound is practically insoluble in water. We elaborated a simple method of preparing its Na-salt (Na-ALA) which proved to be water soluble. It has been demonstrated by ESR spin trapping experiments with DMPO, using the Fenton reaction as the source of OH* free radicals that Na-ALA maintains its OH* free radical scavenging ability: it reacts nearly an order of magnitude faster with these radicals than the spin trap itself. It was tested in two different systems to determine whether Na-ALA was able to protect bovine serum albumin (BSA) against the OH* free radical-induced polymerization and protein oxidation. (i) OH* free radicals were generated by Fenton reaction in the presence of BSA. This protein is polymerized by these radicals shown by the loss of its water solubility; Na-ALA exerted a considerable protective effect against this type of protein damage. (ii) BSA oxidation was induced by Co-gamma irradiation of 80 krad, resulting in a strong increase in the protein carbonyl content. Na-ALA inhibited this carbonyl formation very efficiently. The data suggest that the interaction of the OH radical with Na-ALA takes place on the disulfide group, yielding thiosulfinate or thiosulfonate. The results indicate that the geriatric topical application of Na-ALA may have an established rationale.

Reduction of lipoic acid by lipoamide dehydrogenase

Racemic lipoic acid is therapeutically applied in pathologies in which free radicals are involved. The in vivo reduction of lipoic acid may play an essential role in its antioxidant effect. It was found that mitochondrial lipoamide dehydrogenase (LipDH, EC 1.8.1.4.) reduces the R-enantiomer 28 times faster than the S-enantiomer of lipoic acid. Moreover, it was observed that the metabolites of lipoic acid, bisnor-, tetranor-, and beta-lipoic acid are poor substrates of LipDH. S-lipoic acid inhibits the reduction of the R enantiomer only at relatively high concentrations. The reduction of R-lipoic acid by mitochondria-rich tissues may proceed smoothly, even if the racemic mixture is applied. This is of importance in elucidating the molecular mechanism of the pharmacotherapeutic effect of lipoic acid.

Alpha-lipoic acid reduction by mammalian cells to the dithiol form, and release into the culture medium

Lipoic acid has been reported recently to be an effective antioxidant in biological systems. It may act in vivo through reduction to its dithiol form, dihydrolipoic acid. Using a dual Hg/Au electrode, and HPLC with electrochemical detection, a method was developed which allowed simultaneous measurement of lipoic acid and dihydrolipoic acid, at nanomolar levels. (RS)-alpha-Lipoic acid was added to human cells in tissue culture (Jurkat T-lymphocytes and primary neonatal diploid fibroblasts). Lipoic acid was converted rapidly by the cells to dihydrolipoic acid, which accumulated in the cell pellet. Monitored over a 2-hr interval, dihydrolipoic acid was released, and several-fold more dihydrolipoic acid could be found in the medium than in the pellet.

Growth inhibition of cultured fibroblasts by cobalt and nickel

It is known that tissues surrounding the site of an implanted prosthetic alloy are exposed to increased concentrations of the metals comprising the alloy. However, the exact identity and concentration of such metallic products are usually unknown, thus limiting the possibilities for quantifying any observed toxicological response to the metals. This report describes some of the effects of increased concentrations (7.5-30 microgram/ml; 1-5 x 10(-4)M) Of cobalt (as CoCl2.6H2O) and of nickel (NiCl2.6H2O) on the growth and morphology of cultured mouse fibroblasts. Ultrafiltration experiments indicated that much of the total Co or Ni present in cell culture medium could become bound to macromolecular serum components of the medium. Morphological changes and depressions in the cell growth rate were found to result from high concentrations (15-30 microgram/ml) of either Co or Ni. However, lower concentrations of nickel may have produced some stimulation of cell growth, whereas all concentrations of Co studied were found to depress the rate of cell growth. The growth rate of actively proliferating fibroblasts was quite sensitive to variations in the concentration of either cobalt or nickel. Increased concentrations of cobalt or nickel, therefore, might also affect the normal reconstructive activity of fibroblasts in vivo.

Studies on the nephrotoxicity of p-nitrophenylarsonic acid: changes in rat kidney and urinary enzyme activities following the administration of p-nitrophenylarsonic acid

Histological studies showed that the administration of p-nitrophenylarsonic acid to rats resulted in renal tubular necrosis. The nephrotoxin was administered intraperitoneally and doses greater than 30 mg/kg were found to be fatal. The severity of the renal lesion depended on the amount of the nephrotoxin used. Elevated serum urea levels, urinary protein and volume were recorded over an 8-day period following the injection of the nephrotoxin. These changes were paralleled by an increase in the activity of lactate dehydrogenase, acid and alkaline phosphatase, N-acetyl-beta-glucosaminidase and beta-glucosidase in the urine. beta-Glycosidase activities increased in kidney homogenates, immediately after the injection of the nephrotoxin, but this eventually fell to well below the normal range. Subcellular fractions were prepared from sucrose homogenates by differential centrifugation and beta-glycosidases and cytochrome oxidase were used as enzyme markers. Only minor changes in the activity of cytochrome oxidase activity resulted from the administration of p-nitrophenylarsonic acid. One of the earliest indications of renal damage was a decrease in lysosomal latency. The activities of the lysosomal and soluble enzymes were elevated above normal during the first two days after the injection of p-nitrophenylarsonic acid, but they fell to values, significantly lower than normal, on the third day. The isoenzymic forms of beta-galactosidase, beta-glucosidase and N-acetyl-beta-glucosaminidase in normal and damaged kidneys were studied, using starch gel electrophoresis. The activities of both the lysosomal and the soluble forms of these enzymes decreased following the injection of the nephrotoxin, confirming the results obtained with whole homogenates. The relationship between the changes in renal enzyme activity and urinary enzyme excretion during the nephrotoxic process is discussed.

Some properties of mitochondrial glutathione

1. The presence of GSH in rat liver mitochondria is confirmed. GSH diffuses from the suspended particles in the presence of phosphate but respiratory inhibitors inhibit the diffusion. 2. GSH is oxidised in situ by oxidants including t-butyl hydroperoxide. The products formed include GSSG and GSS-protein mixed disulphides. The oxidation occurs at lower oxidant concentrations if phosphate or oxaloacetate are also present. Respiratory inhibitors abolish their effect. 3. With phosphate, the GSSG produced is found chiefly outside the mitochondria whereas with oxaloacetate, it is found chiefly inside. 4. The GSSG formed by the oxidation is reduced by Krebs-cycle acids with the exception of the ketoacids. Exogenous GSSG is reduced by these substrates only after lysis. Intact particles, however, catalyse the reduction of GSSG by either NADH2 or NADPH2.

Stimulation of globin synthesis: relative responsiveness of reticulocytes and nucleated erythroid cells

The effects of iron, cobalt, hemin, and plasma on hemoglobin synthesis by suspensions of rabbit reticulocytes and nucleated bone marrow cells were studied. L-Leucine-(14)C and sodium pyruvate-3-(14)C were employed to measure globin and heme synthesis, respectively. Normal plasma (or serum) was found to stimulate the rate of globin synthesis in both systems. The stimulatory effects of iron and hemin were additive to those of plasma or serum only in the reticulocytes. Cobaltous ion, at concentrations less than 1.0 mmole/liter, was found to stimulate globin synthesis by reticulocytes as effectively as ferrous ion; cobalt was inhibitory only at concentrations greater than 3.0-5.0 mmoles/liter. Heme synthesis by reticulocytes was inhibited at all concentrations employed (0.2-5.0 mmoles/liter). In bone marrow nucleated erythroid cells, globin synthesis was markedly enhanced by exogenous hemin. In contrast to reticulocytes, however, bone marrow cells were unresponsive to either cobalt or transferrin-bound iron. Possible implications of these findings on regulation of the rate and mechanism of iron uptake and hemoglobin synthesis in vivo are discussed.

The mechanism of disulphide reduction by mitochondria

1. Cystamine was reduced to the corresponding thiol by rat liver mitochondria, even in the presence of rotenone or antimycin A. 2. The reduction of disulphides was stimulated by the accumulation of NADH or by the addition of NADH to osmotically ;shocked' mitochondria. 3. Energy made available by oxidative phosphorylation was not essential for the reduction of disulphides. 4. Cystamine was not reduced during the oxidation of NADH by ultrasonically treated particles, which had lost their capacity for oxidation of alpha-oxo acids. 5. In intact mitochondria, arsenite and other inhibitors of vicinal dithiols caused a decrease in the capacity for reduction of disulphides concomitantly with an inhibition of the oxidation of alpha-oxo acids. 6. Isolated lipoamide dehydrogenase reduced cystamine at the expense of NADH, provided that lipoic acid was also present. 7. It is concluded that in mitochondria the reduction of cystamine and related disulphides is probably brought about by interaction with reduced lipoic acid, generated by the alpha-oxo acid dehydrogenase complexes during the oxidation of alpha-oxo acids or by reaction of lipoamide dehydrogenase with NADH.