Inactivation of renal gamma-glutamyl transferase by 6-diazo-5-oxo-L-norleucylglycine, an inactive precursor of affinity-labeling reagent

The mercapturic acid pathway

The mercapturic acid pathway is a major route for the biotransformation of xenobiotic and endobiotic electrophilic compounds and their metabolites. Mercapturic acids (N-acetyl-l-cysteine S-conjugates) are formed by the sequential action of the glutathione transferases, γ-glutamyltransferases, dipeptidases, and cysteine S-conjugate N-acetyltransferase to yield glutathione S-conjugates, l-cysteinylglycine S-conjugates, l-cysteine S-conjugates, and mercapturic acids; these metabolites constitute a "mercapturomic" profile. Aminoacylases catalyze the hydrolysis of mercapturic acids to form cysteine S-conjugates. Several renal transport systems facilitate the urinary elimination of mercapturic acids; urinary mercapturic acids may serve as biomarkers for exposure to chemicals. Although mercapturic acid formation and elimination is a detoxication reaction, l-cysteine S-conjugates may undergo bioactivation by cysteine S-conjugate β-lyase. Moreover, some l-cysteine S-conjugates, particularly l-cysteinyl-leukotrienes, exert significant pathophysiological effects. Finally, some enzymes of the mercapturic acid pathway are described as the so-called "moonlighting proteins," catalytic proteins that exert multiple biochemical or biophysical functions apart from catalysis.

Edaravone inhibits acute renal injury and cyst formation in cisplatin-treated rat kidney

BACKGROUND

Although cis-diamminedichloroplatinum (II) (cisplatin) is an effective anticancer agent, its clinical use is highly limited predominantly due to its adverse effects on renal functions. The present work examined the therapeutic potential of edaravone, a free radical scavenger, for inhibiting cisplatin-induced renal injury.

METHODS

Edaravone, 3-methyl-1-phenyl-pyrazolin-5-one, was administrated intravenously at a dose of 30 mg/kg of body weight to male Wistar rats (200-220 g). After 30 min, cisplatin was injected intraperitoneally at a dose of 5 mg/kg of body weight. At the indicated times after the treatment, functions and histological changes of the kidney were analyzed. To test the therapeutic potential of edaravone in chemotherapy, its effect on the anticancer action of cisplatin was examined in ascites cancer-bearing rats.

RESULTS

We found that cisplatin rapidly impaired the respiratory function and DNA of mitochondria in renal proximal tubules, thereby inducing apoptosis of tubular epithelial cells within a few days and chronic renal dysfunction associated with multiple cysts one-year after the administration. Administration of edaravone inhibited the cisplatin-induced acute injury of mitochondria and their DNA and renal epithelial cell apoptosis as well as the occurrence of chronic renal dysfunction and multiple cyst formation. The anticancer effect of cisplatin remained unaffected by intravenous administrating of edaravone.

CONCLUSIONS

These results indicate that edaravone may have therapeutic potential for inhibiting the acute and chronic injury of the kidney induced by cisplatin.

Ontogenic changes in hepatic glutathione and metallothionein in rats and the effect of a low-sulphur-containing diet

Metallothionein contains about 30% cysteine and is a major protein in newborn rat liver. This protein and glutathione constitute two major intracellular cysteine pools in newborn rat liver. When pregnant rats were fed on a soya-bean-protein diet, low in sulphur amino acids, the hepatic glutathione levels of the dams were decreased. However, this did not affect the levels of glutathione or metallothionein in the pups. The activity of the glutathione-degrading enzyme gamma-glutamyltransferase (EC 2.3.2.2) in the livers of pups was maximum at birth and gradually decreased with age when the hepatic glutathione was transported to the kidney. In the pups born from dams fed on soya-bean-protein diet the decline in the hepatic enzyme activity was delayed, suggesting a continued degradation of glutathione in the liver. These results suggest that even with a maternal nutritional deficiency of sulphur amino acids, the transfer of cysteine to the fetus is not impaired. However, the hepatic intra-organ degradation of glutathione is continued in these pups for a prolonged period after birth compared with pups born from control mothers. The increased degradation of glutathione in the liver may be essential to meet the requirement of cysteine in pups born from dams fed on the soya-bean-protein diet.

gamma-Glutamyltransferase is not involved in the bulk uptake of amino acids, peptides or gamma-glutamyl-amino acids in yeast (Saccharomyces cerevisiae)

gamma-Glutamyltransferase activity has been measured in yeast (Saccharomyces cerevisiae) and shown to be associated mainly with the membrane fraction. A similar level of activity is found in a wild-type strain and in gap and gpp strains, the latter mutants being defective in the general amino acid and peptide permeases respectively. The activity is inhibited in whole cells by 6-diazo-5-oxo-L-norleucine (N2O-Nle), azaserine and serine-borate complex; this inactivation seemingly acts from without, for it is similar in (i) control and dicyclohexylcarbodi-imide-treated cells and in (ii) the wild-type and a gap mutant, a treatment and a mutation that it has been shown prevents uptake of the inhibitors. Thus a major portion of the gamma-glutamyltransferase activity appears to exist in a membrane-bound form that is orientated with its gamma-glutamyl-binding site facing the outside. Yeast cells in which gamma-glutamyltransferase has been inactivated by N2O-Nle show no significant change in their rates of uptake of a variety of amino acids, dipeptides and gamma-glutamyl-amino acids. The results preclude a major, direct role for gamma-glutamyltransferase in the transport of these substrates.