Effect of nickel(II) on DNA-protein interactions.

Alterations in DNA-protein interactions (DPI) may play an important role in carcinogenesis. Although the mechanism of nickel carcinogenesis is unknown, nickel reportedly affects DPI. A microfiltration, nitrocellulose filter assay was utilized to study DPI in intact Chinese hamster ovary (CHO) cells and in isolated nuclei. Prior to exposure of CHO cells or isolated CHO cell nuclei, DNA and proteins were radiolabeled using 3H-thymidine and 35S-methionine, respectively. Nuclei were exposed to NiCl2 in 10 mM HEPES buffer (pH 6.8). CHO cells were exposed in either complete or a salts-glucose medium. Following exposure, nuclei or cells were incubated at 37 degrees C for 20 min in a high salt lysis solution; aliquots were loaded onto nitrocellulose filters and washed with a low salt solution. DNA (3H) retained on each filter was normalized to protein (35S) bound on the filter. Exposure of either whole cells or isolated nuclei to increasing, noncytotoxic concentrations of NiCl2 resulted in a dose dependent decrease in DPI. The effect of nickel on specific DNA-protein interactions was examined using a band shift assay and a cloned satellite DNA sequence. Nickel inhibited specific protein binding to the satellite DNA probe. The results of these two independent assays, which were conducted at physiological pH, indicate that NiCl2 inhibits specific DNA-protein interactions.

Toxicity and carcinogenicity of nickel compounds.

The toxicity and carcinogenicity of nickel compounds are considered in three broad categories: (1) systemic toxicology, (2) molecular toxicology, and (3) carcinogenicity. The systemic toxicity of nickel compounds is examined based upon human and animal studies. The major organs affected are discussed in three categories: (1) kidney, (2) immune system, and (3) other organs. The second area of concentration is molecular toxicology, which will include a discussion of the chemistry of nickel, its binding to small and large molecular weight ligands, and, finally, its cellular effects. The third major area involves a discussion of the carcinogenicity and genotoxicity of nickel compounds. This section focuses on mechanisms, using studies conducted in vivo and in vitro. It also includes a discussion of the assessment of the carcinogenicity of nickel compounds.

Lead toxicity in chicks: interactions with dietary methionine and choline.

Two factorial experiments were conducted to study the effects of dietary methionine and choline on lead toxicity in chicks. Dietary variables were 0.3 or 0.63% (experiment 1) or 0.23 or 0.75% methionine (experiment 2); 0 or 1000 ppm lead (as Pb acetate X 3H2O); and 1130 or 3300 mg/kg (experiment 1) or 396 or 1266 mg/kg choline (experiment 2). In both experiments, lead depressed growth while methionine stimulated growth. Growth depression by lead was less with methionine-adequate than with methionine-inadequate diets. There were no differences in growth with the choline-marginal or choline-excess diets. In experiment 2, the methionine x lead interaction for growth was observed with choline-adequate but not with choline-inadequate diets. Lead-induced depression of growth was exacerbated by added choline when methionine-inadequate diets were fed. With methionine-adequate diets, choline level had no effect on the lead-induced depression of growth. Hepatic nonprotein sulfhydryl (NPSH) concentrations were increased by both supplemental methionine and lead with no interaction. Choline levels had no effect on NPSH. Dietary methionine significantly lowered Pb concentration of kidney and muscle but not of bone, liver or blood. Choline had no effect on organ Pb concentrations. Methionine, either dietary or in the dosing solution, had no effect on in situ intestinal absorption or 203PbCl2. These results suggest that lead lowers the chick's choline requirement and that the methyl moiety of methionine does not participate directly in lead detoxication. The amelioration of Pb toxicity by methionine appears to be related to increased excretion of Pb.

Modification of lead toxicity and organ distribution by dietary sulfur amino acids in chicks (Gallus domesticus).

Chicks (Gallus domesticus) were fed a basal diet deficient in methionine and total sulfur amino acids with 0 or 1000 ppm added lead for 21 days. Methionine or methionine and cystine addition improved growth regardless of dietary lead level. Cystine addition alone improved growth only when lead was present. Relative inhibition of growth by lead was greater with diets containing no added methionine. Hepatic non-protein sulfhydryl concentration was increased by lead and all amino acid additions. Organ lead concentrations were generally lower with added amino acids. Dietary methionine appears to counteract lead toxicity more effectively than cystine.

[The effects of dietary methionine and glycine on lead toxicity in choline-deficient chicks].

A 2×2×2 factorial experiment was conducted to study the effects of dietary methionine, glycine, and lead (Pb) in cholinedeficient chicks. The variables were: adequate or deficient methionine; adequate or excess glycine; and 0 or 1000 ppm lead (as Pb acetate 3H2O). Methionine stimulated growth when added to the methionine-deficient diets, but the response was greater when supplemental glycine was present. Addition of glycine to the glycine-adequate diets stimulated growth in the presence of adequate but not deficient methionine. The patterns of response to methionine were the same at both 0 and 1000 ppm dietary Pb. Added Pb depressed growth with all diets, but the depression was greater in methionine-deficient than in methionine-adequate diets. Hepatic nonprotein sulfhydryl (NPSH) and glutathione (GSH) concentrations were increased by both supplemental methionine and lead, and the effects were additive. Glycine levels did not significantly alter NPSH and GSH concentrations. Both methionine and glycine lowered Pb concentrations in kidney, and the effects were additive. The results are consistent with previous observations that added methionine ameliorates Pb-induced growth depression with choline-adequate diets, however, this effect is not as pronounced with choline-deficient diets. The results suggest (1) that glycine is limiting for growth in choline-deficient, methionine-adequate diets, and (2) that methionine and glycine may enhance Pb detoxification by different mechanisms.