Toxic effects of mercury(II), cadmium(II) and lead(II) porphyrins on Trypanosoma brucei brucei growth

Predicting the toxic effects of Cu and Cd on Chlamydomonas reinhardtii with a DEBtox model

Predicting the sublethal effects of pollutants to aquatic organism is essential in realistic chemical risk assessment. However, only a few dynamics models for sublethal endpoints are available. Here, we investigated the toxic effects of the essential metal Cu and the nonessential metal Cd on Chlamydomonas reinhardtiiunder both single and combined exposure, compared the effectiveness of different effect endpoints as toxic effect factors, and developed a Dynamic Energy Budget toxicology (DEBtox) model to predict the sublethal effects of Cu and Cd on C. reinhardtii. The results showed that the chlorophyll fluorescence parameter is a better toxic effect indicator than others for short-term exposure (<24 h), while algal cell growth is preferred for long-term exposure (2-6 days). The developed DEBtox model could successfully predict single metal toxicity to C. reinhardtii, while the combined metal DEBtox model slightly overestimates the joint toxicity of Cu-Cd due to the antagonistic effect of Cu-Cd on C. reinhardtii. This study is helpful to understanding and better predictions of metal sublethal toxic effects on aquatic organisms.

Effect of PbII on the Secondary Structure and Biological Activity of Trypsin

The effects of Pb(II) on the secondary structure and biological activity of trypsin have been examined by monitoring changes in its conductivity and IR and circular dichroism (CD) spectra. The results show that Pb(II) reacts with trypsin, and that the binding sites might be -OH and -NH groups in pepsin. The CD spectra indicate that interaction with Pb(II) significantly affects the secondary structure of trypsin, the beta-sheet-structure content being increased by about 42%, whilst those of alpha-helix and beta-turn structures are decreased by 13% and 21%, respectively. The results clearly demonstrate that Pb(II) affects the biological activity of trypsin by modifying its secondary structure. Most interesting is that Pb(II) up-regulates the activity of trypsin at low concentrations while down-regulating it at high concentrations.

In vitro toxicity of palladium(II) and gold(III) porphyrins and their aqueous metal ion counterparts on Trypanosoma brucei brucei growth

The trypanocidal effects of aqueous gold(III) and palladium(II) and their metalloporphyrin derivatives on Trypanosoma brucei brucei growth in culture have been studied using an Alamar Blue indicator assay. All the experiments were conducted in the dark. As previously described for mercury(II), cadmium(II) and lead(II) porphyrins [Chem.-Biol. Interact. 139 (2002) 177], the toxicity of the metalloporphyrin complex of palladium(II) to T. b. brucei parasites was much higher compared to the aqueous free palladium(II) and free base porphyrin. Palladium(II) porphyrin, free palladium(II), and the free base porphyrin were trypanocidal to T. b. brucei at concentrations >1.5 x 10(-6), >6.1 x 10(-6) and >1.9 x 10(-5) M, respectively. While gold(III) porphyrin was effective against the parasites at concentrations >4.8 x 10(-6) M, its aqueous gold(III) was toxic at concentrations as low as 2.0 x 10(-7) M due to the generation of free radicals in the presence of this metal ion which enhanced its toxicity to the T. b. brucei parasites. Although some cell division was observed in some of the cells treated with palladium(II) porphyrin, some dividing cells had no nucleus due to unequal division and delivery of the nuclei into the daughter cells. As a result, the rate of cell division decreased with time and cell death occurred within 24 h. Interestingly, trypanosomes treated with metalloporphyrin complexes displayed different morphological features from those cells treated with free base porphyrin or metal ions. Of all the porphyrins and free metal ions tested, only mercury(II) porphyrin and aqueous gold(III) ion were toxic to the trypanosomes in the 10(-7) M range. The chemotherapeutic potential of these observations is discussed.

Effects of Cd+2, Cu+2, Ba+2 and Co+2 ions on Entamoeba histolytica cysts

AIM: The effects of cobalt, copper, cadmium and barium ions on the cysts of Entamoeba histolytica (E. histolytica), an amebic dysentery agent, cultured in Robinson medium were investigated.

METHODS: E. histolytica cysts and trophozoites isolated from a patient with amebiasis were cultivated in the medium, incubated at 37 °C for a period of 4 days and 40 × 10⁴/ml amebic cysts were then transferred to a fresh medium. At the second stage, 0.05, 0.1 and 0.2 mM of selected metal ions were added to the medium, and the effects of these ions on parasitic reproduction compared with the control group were observed.

RESULTS: It was determined that the number of living parasites in all the groups containing metal ions decreased significantly starting from 30 minutes (P < 0.01). CuCl₂ showed the highest lethal effect on E. histolytica cysts, whereas the lowest lethal effect was observed with CoCl₂. It was also seen that the number of living cells was decreased as the ion concentration and exposure time were increased, and that there were no living parasites in the medium at the end of 24 h (P < 0.01).

CONCLUSION: It may be stated that the effect of ever-increasing contamination of the environment with metal waste materials on parasites should be investigated further.

Enhanced conformational changes in DNA in the presence of mercury(II), cadmium(II) and lead(II) porphyrins

The interactions of the metalloporphyrins of tetrakis (1-methylpyridinium-4yl)porphyrin ([M(TMPyP)](4+)) where M=Hg(II), Cd(II) and Pb(II)) with pBluescript II plasmid DNA have been studied by the measurement of circular dichroism (CD), UV-visible and fluorescence spectra at 0.1 M NaNO(3), pH 7.5 and 25 degrees C. The CD spectra of the DNA changed quite significantly, with the conformational changes in the presence of the metalloporphyrins being much more enhanced compared to that of their free metal ion counterparts. The conformational changes in DNA upon binding to the Hg(II) porphyrin and Hg(II) were, however, different from those of the Cd(II) porphyrin, Pb(II) porphyrin, Pb(II), Cd(II) and H(2)(TMPyP)(4+). In the concentration range of 0-2.30 x 10(-5) M of DNA, the absorption spectra of H(2)(TMPyP)(4+) showed substantial hypochromicity at 423 nm and a red shift of Deltalambda=16 nm in the presence of DNA whereas the Hg(II)-, Pb(II)- and Cd(II) porphyrins showed blue shifts of absorption maximum wavelengths of Deltalambda=-17 nm, Deltalambda=-35 nm and Deltalambda=-4.5 nm, respectively. Furthermore, the shifted absorption maximum wavelengths/nm of the porphyrins in excess amount of DNA were comparable; 438, 439, 440 and 440 for H(2)(TMPyP)(4+), Hg(II)-, Pb(II)- and Cd(II) porphyrins, respectively. The changes in absorption spectra for Hg(II)-, Pb(II)- and Cd(II) porphyrins revealed that these metalloporphyrins dissociated upon binding to DNA which was confirmed by CD as well as fluorescence spectra. The CD results, UV-Vis and fluorescence data indicate that the metalloporphyrins interact differently with DNA based on their binding modes. And the enhanced changes in conformation of DNA in the presence of the metalloporphyrins are due to the synergistic effects of the simultaneous binding of the metal ions and the free base porphyrin to DNA compared to their free metal ion counterparts: [M(TMPyP)](4+)+DNA+2H(+) right harpoon over left harpoon [M(II)(DNA)H(2)(TMPyP)(4+)]. The detailed equilibrium reactions have been described along with suggestions of possible applications in the medical and biological fields.