T-2 mycotoxin inhibits mitochondrial protein synthesis

We investigated the effect of T-2 toxin on rat liver mitochondrial protein synthesis. Isolated rat liver mitochondria were supplemented with an S-100 supernatant from rat liver and an external ATP-generating system. We used an in vitro assay employing cycloheximide, an inhibitor of cytoplasmic protein synthesis, and chloramphenicol, an inhibitor of mitochondrial protein synthesis, to distinguish mitochondrial protein synthesis from the cytoplasmic process. Amino acid incorporation into mitochondria was dependent on the concentration of mitochondria and was inhibited by chloramphenicol. The rate of uptake of [3H]leucine into mitochondrial protein was unaffected by the addition of T-2 toxin and was not a rate-limiting step in incorporation. However, 0.02 micrograms/ml of T-2 toxin decreased the rate of protein synthesis by isolated mitochondria by 50%. The degree of protein synthesis inhibition correlated with the amount of T-2 toxin taken up by the mitochondria. While T-2 toxin is known to inhibit eukaryotic protein synthesis, this is the first time T-2 was shown to inhibit mitochondrial protein synthesis.

Hepatic metallothionein induction in inflammation

Numerous chemically distinct phlogistic substances have been shown to induce hepatic metallothionein-Zn (MT) accumulation when administered to rats. These findings suggest that induction of this cysteine-rich metalloprotein occurs through the action of some common mediator(s). Possible mediators include substances such as leukocytic endogenous mediator (LEM) and/or hormones known to influence hepatic protein synthesis. Studies were performed to examine further the mechanism(s) and potential mediators involved in endotoxin-induced MT accumulation. Additionally, the studies were performed to determine the possible involvement of genetic factors, which reportedly influence LEM production, in the induced MT response. Endotoxin (ET) was administered ip to rats and to EP-resistant, C3H/HeJ, and susceptible, C3Heb/FeJ, stains of mice. ET induced hypozincemia, hyperglucagonemia, and increased MT concentrations in rats. ET induced hypozincemia and MT accumulation to the same extent in both strains of mice. The induction of tolerance in rats to Zn depressing activity of ET also prevented hyperglucagonemia and additional accumulation of MT. Results suggest that glucagon, but not LEM, may be a common mediator in MT response during inflammatory stress.

Effect of adrenalectomy on cadmium- and turpentine-induced hepatic synthesis of metallothionein and alpha 2-macrofetoprotein in the rat

Recent reports have strongly implicated glucocorticoids in the induction of hepatic metallothionein synthesis and hypozincemia which occurs in certain pathophysiologic conditions. Studies were performed in rats to determine the effect of adrenalectomy and glucocorticoid treatment on the hepatic accumulation of metallothionein subsequent to the administration of cadmium and turpentine, two diverse substances known to induce hypozincemia and hepatic synthesis of metallothionein as well as alpha 2-macrofetoprotein in intact rats. By 24 h, both substances induced significant hypozincemia, hepatic metallothionein accumulation, and a severe tissue inflammatory response in adrenalectomized rats. Adrenalectomy only prevented the increase in plasma alpha 2-macrofetoprotein concentration. Results indicate that hepatic synthesis of alpha 2-macrofetoprotein, but not metallothionein, is mediated by adrenal hormones. Thus, glucocorticoids do not play a "vital" role in hepatic metallothionein accumulation or hypozincemia induced by inflammatory stress, as previously postulated.

Involvement of hepatic metallothioneins in hypozincemia associated with bacterial infection

Hypozincemia was induced in rats by Salmonella typhimurium and live vaccine strain Francisella tularensis (LVS) infections. Hepatic synthesis of zinc-binding proteins (ZBP) was studied in order to elucidate the mechanisms involved in the redistribution of zinc from plasma to liver occurring during infectious illness. ZBP, labeled in vivo with 65Zn, were isolated and identified as metallothioneins based, in part, on their heat stability, dimorphism, and amino acid composition. Cysteine was the major amino acid found in both forms of metallothionein and constituted 28-31% of total residues. The apparent half-life of these proteins as measured by disappearance of 65Zn was determined to be 19 h in a relatively mild infection (LVS) and 38 h in a more severe S. typhimurium infection. Results provide evidence that metallothioneins not only have the previously postulated regulatory role in normal zinc homeostasis but are intimately involved in the zinc redistribution occurring during the acute stage of infectious illness.

Role of zinc in the abatement of hepatocellular damage and mortality incidence in endotoxemic rats

Intraperitoneal administration of zinc (ZnIP) as zinc chloride prior to or simultaneously with a lethal quantity of intraperitoneally administered Salmonella typhimurium endotoxin significantly protected rats against toxin-induced mortality and hepatocellular damage. Pretreatment with amounts of zinc chloride ranging from 0.4 to 2.0 mg/100 g of body weight resulted in 80 to 100% survival compared with 10% survival in untreated control rats at 24 h after endotoxin treatment. Zinc chloride treatment in excess of 2.0 mg/100 g of body weight appeared to be toxic and provided diminished protection. In contrast with the protection obtained with ZnIP, intravenously administered zinc did not provide protection. The effectiveness of ZnIP to enhance survival if it was given after endotoxin was greatly diminished as a function of time after endotoxin. The extent of hepatocellular damage was assessed at various times after endotoxin administration in ZnIP-treated and untreated rats by measurement of plasma ornithine carbamoyltransferase activity and histological examination of liver sections. Endotoxin absorption from the peritoneal cavity and hepatic uptake were studied by using 51Cr-labeled endotoxin. ZnIP pretreatment significantly reduced 51Cr-labeled endotoxin content of blood and liver when compared to untreated controls, and effectively prevented endotoxin-induced elevations in plasma ornithine carbamoyltransferase activity and hepatic tissue necrosis. These data indicate that protection afforded by ZnIP treatment results as a consequence of the ability of zinc to diminish absorption of the toxin from the peritoneal cavity and subsequent hepatic uptake.

Improved continuous-flow method for detemination of total serum hexosamines

We describe an automated determination of serum hexosamine by the Elson-Morgan reaction, together with reagent modifications that minimiz interference from amino acids and sugars present in acid hydrolysates of sera. We used a novel 15-min autoclave procedure for the acid hydrolysis of sera before analysis to facilitate the detemination as compared to the 4-h hydrolysis used in the conventional manual method. Results correlated well (r = 0.906) with those obtained by the corresponding manual method.

Improved continuous-flow method for detemination of total serum hexosamines

We describe an automated determination of serum hexosamine by the Elson-Morgan reaction, together with reagent modifications that minimiz interference from amino acids and sugars present in acid hydrolysates of sera. We used a novel 15-min autoclave procedure for the acid hydrolysis of sera before analysis to facilitate the detemination as compared to the 4-h hydrolysis used in the conventional manual method. Results correlated well (r = 0.906) with those obtained by the corresponding manual method.

Chronic depression of serum concentrations of sialic acid in alloxan-induced diabetic rats

This study was performed to determine whether alloxan treatment of rats alters concentrations of the terminal carbohydrate residues, L-fucose and sialic acid, of serum glycoproteins. Results indicate that in the uncompensated diabetic rat, chronic depression of serum sialic acid concentration occurred with no apparent alteration in the concentration of L-fucose. The depression in sialic acid concentration may be attributed, in part, to decreased activities of hepatic enzymes involved in sialic acid synthesis similar to those observed by others after treatment of rats with the diabetogenic agent streptozotocin. The lack of any significant alteration in the concentration of L-fucose fails to confirm, in the experimental diabetic rat, the increased protein-bound fucose values reported in human diabetics. Administration of insulin was not effective in modifying the sialic acid response after alloxan treatment.