The force of the spontaneously contracting zebrafish heart, in the assessment of cardiovascular toxicity: application on adriamycin.

The heart of the zebrafish has been used extensively to assess the cardiotoxic effect of compounds, using the frequency of heart contractions as the main index of cardiac response to drugs. In this study, the force and the frequency generated by the spontaneously contracting zebrafish heart, isolated in saline, were found to be 0.87 ± 0.05 mN and 1.54 ± 0.03 Hz (n=6) respectively within the first hour of recording. Both values of force and frequency remained constant for over 8h. The advantage of prolonged vitality in the assessment of cardiovascular toxicity was shown using the well-known anticancer drug adriamycin, which has severe cardiotoxic side effects. At 10.0 µM there was a 21.05 ± 4.42% (p=0.02, n=4) decrease in the force of contraction, while the frequency was not affected after 3h treatment (p>0.05). At 50.0 and 100.0 µM there was a 33.24 ± 3.0 and 46.6 ± 4.80% irreversible decrease in force (p<0.05, n=4), while a 18.02 ± 4.07% and 16.16 ± 4.07% reversible increase was observed in the frequency (p=0.02, n=4). These contradictory positive chronotropic and negative inotropic responses indicate the strong inhibitory effect of adriamycin on ventricular cardiomyocytes and its excitatory effects on auto-rhythmical pacemaker cells. If heart frequency was the only parameter used to assess the cardiotoxic effect of adriamycin, at the above range of concentrations, this compound would have been classified as non-cardiotoxic.

In vitro assessment of the effects of cadmium and zinc on mammalian nerve fibres.

Zinc and cadmium are environmental contaminants that have a wide range of effects on the nervous system, but zinc is also considered to be an important metal in the human body. In this study the effect of CdCl(2) and ZnCl(2), at concentrations of 50,150, 250 and 500 microM, on the nerve fibres of the sciatic nerve of the rat isolated in a three-chamber recording bath were studied. At the same concentrations, CdCl(2) and ZnCl(2) were found to have almost the same inhibitory effect on the compound action potential (CAP) of the nerve fibres. Their concentration-effect curves almost overlap and there was no significant difference in their EC(50) which for CdCl(2) is 250.1+/-18 microM (n=5) and for ZnCl(2) is 282.2+/-25 microM (n=5) correspondingly (P>0.05). The no-observed-effect concentration (NOEC) was estimated to be 50-100 microM for both metals. The identical inhibitory effect of both metals on the sciatic nerve fibres indicates a common mode of action which is related to their potential to generate reactive oxygen species (ROS).

In vitro assessment of the neurotoxic and neuroprotective effects of N-acetyl-L-cysteine (NAC) on the rat sciatic nerve fibers.

N-acetyl-L-cysteine (NAC), at a concentration of 1-60mM, has been previously used extensively for protection in a variety of cell cultures against the deleterious effects of various compounds. The results of this in vitro study show that NAC has certain unusual effects on the evoked compound action potential (CAP) of the rat sciatic nerve fibers. Firstly, at concentrations of 5.0, 3.5 and 2.5mM, concentrations used by others as a protectant for cell cultures, NAC inhibits the action potentials of the sciatic nerve fibers completely in a concentration-dependent manner within a few minutes or hours (2.5mM). Secondly, the acute inhibitory action of NAC on the CAP of the nerve fibers was not spontaneously reversible, but as soon as NAC was replaced with saline there was a partial (approximately 75%) recovery in the function of the nerve fibers. Thirdly, the no observed effect concentration for NAC was estimated to be 1mM. The paradox is that NAC at 1 mM not only had no effect on the nerve fibers, but it became an excellent neuroprotective compound, giving almost 100% neuroprotection against cadmium-induced neurotoxicity. The results show a possible effect of NAC on voltage-gated sodium and potassium channels. The observed neuroprotective-neurotoxic properties of NAC require careful reconsideration of its use in either in vitro studies or in vivo pharmaceutical applications.

Comparison of two screening bioassays, based on the frog sciatic nerve and yeast cells, for the assessment of herbicide toxicity.

Two different test systems, one based on the isolated sciatic nerve of an amphibian and the other on a microbial eukaryote, were used for the assessment of herbicide toxicity. More specifically, we determined the deleterious effects of increasing concentrations of herbicides of different chemical classes (phenoxyacetic acids, triazines, and acetamides), and of 2,4-dichlorophenol (2,4-DCP), a degradation product of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), on electrophysiological parameters and the vitality of the axons of the isolated sciatic nerve of the frog (Rana ridibunda) and on the growth curve of the yeast Saccharomyces cerevisiae based on microtiter plate susceptibility assays. The no-observed-effect-concentration (NOEC), defined as the maximum concentration of the tested compound that has no effect on these biological parameters, was estimated. In spite of the different methodological approaches and biological systems compared, the NOEC values were identical and correlated with the lipophilicity of the tested compounds. The relative toxicity established here, 2,4-DCP > alachlor, metolachlor >> metribuzin > 2,4-D, 2-methyl-4-chlorophenoxyacetic acid (MCPA), correlates with the toxicity indexes reported in the literature for freshwater organisms. Based on these results, we suggest that the relatively simple, rapid, and low-cost test systems examined here may be of interest as alternative or complementary tests for toxicological assessment of herbicides.