Effect of oxidative sulfitolysis of disulfide bonds of bovine serum albumin on its structural properties: a physiochemical study

The effect of S-S bond cleavage of bovine serum albumin (BSA) on some of its structural properties, including solubility, viscosity, and conformation, were investigated. Cleavage of S-S bonds decreased the solubility of serum albumin and also shifted its isoelectric point to lower pH values. S-S bond cleavage resulted in changes in shape and hydrodynamic volume of the protein, increasing the specific viscosity, with cleavage of up to 14 S-S bonds, followed by a decrease with further cleavage. Both UV difference and fluorescence spectral measurements indicated that conformational flexibility increases with S-S bond cleavage. Secondary structure estimations by far UV-CD suggested a gradual decrease in alpha-helical content of the protein with progressive cleavage of its S-S bonds. However, fully S-S bond cleaved protein maintained some alpha-helical structure. Sulfitolysis of the protein also decreased its 1,8-anilino-naphthalene sulfonate-binding ability.

Glutathione is involved in the early cadmium cytotoxic response in human lung carcinoma cells

Depletion of cellular glutathione (GSH) has been shown to sensitize A549-T27 human tumor cells to the cytotoxic effects of Cd2+. In this study the temporal and quantitative relationships between reduced cellular GSH levels and cadmium cytotoxic response in these cells were further investigated. Exposure of A549-T27 cells to 10 mM buthionine sulfoximine (BSO) for 8 h decreased their GSH level by 65%. This GSH level remained relatively constant for 8 h in the presence or absence of BSO, but recovered to 83% of the normal cellular level 24 h after removal of BSO. Exposure to 5 microM Cd2+ for 8 h did not significantly change cellular GSH levels. Pretreatment of the A549-T27 cells with 10 mM BSO for 8 h and subsequent exposure of the cells to Cd2+ for 10 days, with or without concurrent treatment of 10 mM BSO during the first 8 h of Cd2+ exposure, resulted in disappearance of the 5 microM Cd2+ threshold for cytotoxic response and reduction of the LC50 from 31 microM Cd2+ to 21 microM. Similar results were obtained when BSO pretreated cells were exposed to Cd2+ for 8 h. The threshold for cytotoxic response of 10 microM Cd2+ disappeared and the LC50 was reduced from 60 microM to 29 microM Cd2+ (with concurrent BSO treatment) and 30 microM (BSO pretreatment only). The results show that GSH plays an important role in early cellular protective responses to Cd2+.

Effect of cellular glutathione depletion on cadmium-induced cytotoxicity in human lung carcinoma cells

The effect of glutathione depletion on cellular toxicity of cadmium was investigated in a subpopulation (T27) of human lung carcinoma A549 cells with coordinately high glutathione levels and Cd++-resistance. Cellular glutathione levels were depleted by exposing the cells to diethyl maleate or buthionine sulfoximine. Depletion was dose-dependent. Exposure of the cells to 0.5 mM diethyl maleate for 4 hours or to 10 mM buthionine sulfoximine for 8 hours eliminated the threshold for Cd++ cytotoxic effect and decreased the LD50S. Cells that were pretreated with 0.5 mM diethyl maleate or 10 mM buthionine sulfoximine and then exposed to these same concentrations of diethyl maleate or buthionine sulfoximine during the subsequent assay for colony forming efficiency produced no colonies, reflecting an enhanced sensitivity to these agents at low cell density. Diethyl maleate was found to be more cytotoxic than buthionine sulfoximine. Synergistic cytotoxic effects were observed in the response of diethyl maleate pretreated cells exposed to Cd++. Thus the results demonstrated that depletion of most cellular glutathione in A549-T27 cells prior to Cd++ exposure sensitizes them to the agent's cytotoxic effects. Glutathione thus may be involved in modulating the early cellular Cd++ cytotoxic response. Comparison of reduced glutathione levels and of Cd++ cytotoxic responses in buthionine sulfoximine-treated A549-T27 cells with those levels in other, untreated normal and tumor-derived cells suggests that the higher level of glutathione in A549-T27 is not the sole determinant of its higher level of Cd++ resistance.

Effects of cefonicid and other cephalosporin antibiotics on male sexual development in rats

The purpose of this study was to determine whether cefonicid, a cephalosporin antibiotic with a modified N-methylthiotetrazole (MTT) side chain, caused testicular toxicity when subcutaneously administered to Sprague-Dawley male rats from days 6 to 36 postpartum at doses of 50 to 1,000 mg/kg per day. Moxalactam (a cephamycin antibiotic which will be referred to as a cephalosporin for convenience throughout), which contains the MTT side chain, was used as a positive control and was administered at 100 to 1,000 mg/kg per day, and cephalothin, which lacks an MTT side chain, was used as the negative control at 1,000 mg/kg per day. Moxalactam caused a significant reduction in testicular and seminal vesicle weights in 37-day-old animals, and histological examination revealed bilateral multifocal atrophy of the seminiferous tubules at all dose levels. Animals reared to reproductive maturity had significant deficits in fertility, and histological examination revealed multifocal or diffuse atrophy of the seminiferous tubules at all doses with a severity greater than that observed in the 37-day-old animals. The histological findings were confirmed by marked reductions in testicular sperm production rates and cauda epididymal sperm numbers. Cephalothin and cefonicid had no treatment-related adverse effects on the sexual maturation of prepubertal, juvenile, or adult males. The absence (in cephalothin) or modification (in cefonicid) of the MTT side chain was not associated with adverse reproductive effects. The relevance of these findings to humans in prenatal and prepubertal stages of life cannot be determined at this time.

Strain differences in response of Sprague-Dawley and Long Evans Hooded rats to the teratogen nitrofen

Administration of nitrofen (2,4-dichloro-4'-nitrodiphenyl ether) during organogenesis in rodents produces neonatal lethality accompanied by lung hypoplasia, diaphragmatic hernias, heart anomalies, and hydronephrosis. Different strains of rats, Long Evans Hooded (LEH) and Sprague-Dawley (SD), are reported to have different malformation responses to prenatal exposure, which could be due to true strain differences, to different levels and times of exposure, or to the use of different methods for detecting visceral malformations. In the present study, LEH, SD, and "virus-antibody-negative" SD (VAN-SD) rats were identically exposed to 0, 6.25, 12.5, or 25 mg/kg/day of nitrofen by gavage in corn oil on days 6 15 of gestation. At term, half of the litter was examined by the Wilson method of razorblade sectioning and the remainder by a modified Staples method of fresh visceral examination. The two methods were equally sensitive for detecting diaphragm, kidney, and lung anomalies, whereas heart malformations were more frequently identified with fresh visceral examination. The frequency of total malformations did not vary across strains at any dose, but there were substantial differences in the pattern of malformations in each strain. SD and VAN-SD rats responded similarly for all malformations, but had significantly higher incidences of diaphragm and lung anomalies than LEH rats. Conversely, LEH rats had significantly elevated levels of kidney anomalies compared to SD and VAN-SD rats, whereas frequency of heart malformations was low and comparable across strains. These results suggest that true strain differences exist in the pattern of malformation produced by prenatal exposure to nitrofen that may be based on genetic differences in embryonic susceptibility.

Changes in nucleolar proteins and their phosphorylation patterns during liver regeneration

Two-dimensional polyacrylamide gel electrophoresis of nucleolar proteins of rat liver revealed marked changes at various times after partial hepatectomy. Some of the non-histone protein spots including A11, A24, A25, C13, and C14 decreased in size and density. Others, including A15, B13, B16, B18, B24-25, B27, B33, B34, C1, C2, C8, C11, C17, and C23-24 were markedly increased in size and density. In vitro labeling of the nucleoli using [gamma-32P]ATP and subsequent analysis of the proteins by two-dimensional gel electrophoresis and autoradiography indicated that the uptake of 32P into proteins increased greatly during regeneration. In addition, the relative labelling of various spots changed throughout the regeneration process. With spot B33 as a reference, there was increased labeling of spots A1P, B2, B5, B24-25, C2, and C23-24 at 8 hours after hepatectomy. On the other hand, the labeling of spots A8P, A16, A20, B9, and B13 decreased at 8 hours after hepatectomy. Since the primary role of the nucleolus is the snythesis of ribosomal precursors, these changes in protein content and phosphorylation are presumably primarily associated with the increased processing and transport of peribosomal ribonucleoproteins in regenerating liver.

Nucleolar phosphoproteins of normal rat liver and Novikoff hepatoma ascites cells

The nucleolar acid-soluble proteins from normal rat liver and Novikoff hepatoma ascites cells were labeled in vivo for 2 hr after the injection of [32P]orthophosphate and in vitro with [gamma-32P]adenosine triphosphate in systems containing 0.25 M sucrose, 5 mM MgCl2, 12.5 mM NaCl, and 0.05 M Tris-HCl buffer, pH 7.3, AT 37 DEGREES. Two-dimensional polyacrylamide gel electrophoresis and autoradiography showed that approximately 40 and 20 protein spots were labeled in vivo and in vitro, respectively. There were some marked differences in labeling in vivo between normal rat liver and Novikoff hepatoma acid-soluble nucleolar proteins. By 32P analysis of gel slices, the proportion of the total 32P incorporated into protein Spot A1-4 was greater in normal liver, and the proportion of 32P incorporated into some high-molecular-weight protein spots, such C23-24 and C26-27, was greater in the Novikoff hepatoma ascites cells. With the in vitro incubation system, the 32P uptake per mg protein was about twice as high in Novikoff hepatoma nucleolar proteins as in normal rat liver nucleolar proteins but, generally, the same proteins were labeled in both tissues.