Effect of cadmium on collagen content and solubility in rat bone.

The toxic action of cadmium in the bone tissue is known, but its mechanisms are still unexplained. We examined whether Cd influences collagen content and its solubility in the femoral bone of three-week-old female rats exposed to 5 or 50 mg Cd/l in drinking water. Non-cross linked collagen was extracted with 0.5 M acetic acid, and two acid-insoluble collagen fractions were extracted with pepsin and 4.0 M guanidine hydrochloride, respectively. SDS/PAGE showed the presence of two collagen types, I and V, in all three extracted fractions. Exposure of rats to Cd for 6 months increased the amount of acid-soluble collagens type I and V and decreased the level of acid-insoluble collagens. The amount of total collagen extracted from the bones of rats exposed to 50 mg Cd/l was reduced by about 14% as compared to control and those intoxicated with 5 mg Cd/l. The solubility of type I bone collagen (determined as the percentage of acetic-soluble fraction of total collagen) was increased 2.9- and 3.0-fold in rats intoxicated with 5 and 50 mg Cd/l, respectively. Similarly, the solubility of type V collagen was increased 2.3- and 2.7-fold, respectively. Our results indicate that Cd treatment affects bone collagen by decreasing its content and increasing its solubility.

Elongation factor 2 as a target for selective inhibition of protein synthesis in vitro by the novel aromatic bisamidine.

The effect of the novel aromatic bisamidine 1 on protein synthesis in cell-free translational system isolated from rat livers was studied. The bisamidine 1 caused inhibition of [14C]leucine incorporation into proteins proportionally to its concentration. To establish a precise mechanism of inhibition, we evaluated the effect of the bisamidine 1 on the isolated ribosomes and purified to homogeneity elongation factors. Preincubation of the bisamidine 1 with ribosomes resulted in partial inhibition of their activity in whole elongation system. The eucaryotic elongation factor 1 (eEF-1) was not significantly affected by the bisamidine 1. In contrast to eEF-1, the bisamidine 1 preincubated with the eucaryotic elongation factor 2 (eEF-2) caused total inhibition of its activity in the translocation process. The inhibitory effect of the bisamidine 1 on eEF-2 activity was confirmed in diphtheria toxin-dependent ADP-ribosylation reaction. The results suggest a high action specificity of the bisamidine 1 as potential anticancer drug, since the primary target seems to be highly conserved protein-elongation factor 2.