Quantitative structure-activity relationships for the toxicity of nitrobenzenes to Tetrahymena thermophila.

In this study IGC50 (50% inhibitory growth concentration) values of 26 nitrobenzenes were determined for population growth endpoint of Tetrahymena thermophila. The toxicity order of the observed compounds has been found as follows: dinitro compounds > mono-nitro compounds; dichloronitrobenzenes > monochloronitrobenzenes; and meta-substituted nitrobenzenes > ortho-/para-substituted nitrobenzenes (NT, NPh, NAnis) except for the dinitrobenzenes and nitroanilines (DNB, NAn). Quantitative structure activity relationships (QSARs) were developed using log of the inverse of the IGC50 (logIGC50(-1)) in mole liter as the dependent variable and six molecular descriptors--logP, 1X(V), I, K alpha, sigma sigma- and E(LUMO) as the independent variables. Through multiplicate regression analysis, one best equation was obtained: log IGC50(-1) = 2.93 + 0.830sigma sigma- + 0.350I, n = 26, r = 0.923, r2 = 0.852, s = 0.265, f = 66.4 The equation was used to estimate IGC50 for seven analogues.

Progress in an ecotoxicological standard protocol with protozoa: results from a pilot ring test with Tetrahymena pyriformis.

The aim of this project was to develop a standardized multigeneration growth inhibition test protocol to assess the sublethal effects of industrial chemicals and pesticides on protozoans. The inclusion of a test with protozoa would be an ecologically relevant supplement to the existing basic set in aquatic toxicity testing. The different aspects evaluated in the pilot ring study include: two media, two volumes, two end points and two different methods to measure the cell density. Taking into account the aim to develop a simple, sensitive, reproducible and cost effective test, recommendations are made for a standardized protocol.

Toxicological comparisons of Tetrahymena species, end points and growth media: supplementary investigations to the pilot ring test.

Parallel to an international Pilot Ring Test to standardize a mutigeneration test protocol with the protozoon Tetrahymena pyriformis supplementary investigations were made. Effects on growth rate and 46 h population density were measured using an extended set of 12 chemicals, a further Tetrahymena-species (T. thermophila) and 4 different media (axenic and bacteria based). Results are compared for sensitivity with effects on additional end points (chemosensory response, respiration and vitality). Both species exhibit similar sensitivity towards the chemicals. In some cases the media composition influenced the toxic potential of chemicals. Both growth parameters proved to be a sensitive integral end point for toxicological studies, confirming the one point, photometric measurement of population density after 46 hours in axenic (preferably proteose peptone-) medium an obvious choice for a standard test procedure.

Interaction with functional membrane proteins--a common mechanism of toxicity for lipophilic environmental chemicals?

1. The effects of several phenols, anilines and aliphatic alcohols on yeast plasma membrane H(+)-ATPase and purine transport system as well as on Na+, K(+)-ATPase and adenosine uptake by Chinese hamster ovary cells (CHO) were investigated. 2. In all cases an inhibition was observed, which could be correlated with the octanol/water partition coefficients of the substances tested, thus making quantitative structure-activity predictions possible. 3. The observed effects correlated well with the influence of the chemicals on cell growth. 4. The results suggest a common mechanism of toxicity by the action of hydrophobic xenobiotics on biomembranes.

The comparative influence of substituted phenols (especially chlorophenols) on yeast cells assayed by electro-rotation and other methods.

The toxicity of 31 phenols was studied by electro-rotation of yeast cells. Control yeast cells show both anti-field and co-field rotation, depending upon the field frequency applied. After treatment with supra-threshold amounts of phenols the anti-field rotation is weakened or abolished and a stronger co-field rotation can be seen. The proportion of cells showing the co-field rotation was found to be a sensitive measure of toxicity. Doses of 2.2 mumol/l of pentachlorophenol, or of 0.3 mumol/l of pentabromophenol were detectable after 3 h incubation at pH 4.0. At a given pH, the toxicity of the chlorophenols correlated extremely well with their octanol:water partition coefficients (Pow). The complete set of phenols showed fair overall correlation with Pow, but less good correlation with their acidity constants (pKa). In particular the toxicity of a given phenol was less than predicted from its pKa if the incubation pH was higher than the pKa. Biochemical assays on 23 of the phenols showed that the rotational sensitivity runs closely parallel to the sensitivities of cell growth rate and of the plasmamembrane ATPase, but less closely to the inhibition of purine incorporation. It appears that the electro-rotation method provides a useful and rapid test for the presence of organic ecotoxins. The test enables us to distinguish differences between single cells, and is comparable in sensitivity to biochemical tests that use vesicles or homogenates derived from a cell population.

Acrodermatitis enteropathica. II. Zinc deficiency and ultrastructural findings.

The basic defect in acrodermatitis enteropathica (A.E.) is zinc deficiency caused by zinc malabsorption. The clinical symptoms disappear and serum zinc levels normalize after oral treatment with zinc. A report is given on two siblings suffering from A.E., both treated with oxyquinolines for a long period with changing clinical success. A permanent clinical remission could be achieved by treatment with zinc-sulphate at doses of 110-220 mg daily. The serum zinc levels normalized. The correlation between the zinc concentration of the hair and the kind of therapy was not very close. As we have shown in our first communication, the Paneth cells of the intestinal mucosa display ultrastructural changes in form of an unhomogeneous structure of the cytoplasm, formation of giant granules, and inclusion bodies. The zinc-therapy led to a complete normalization of the pathological changes in the Paneth cells. Thus, the changes in the Paneth cells in A.E. are the result and not the cause of zinc deficiency.

Acrodermatitis enteropathica: recent findings concerning clinical features, pathogenesis, diagnosis and therapy.

Acrodermatitis enteropathica (AE) was diagnosed in 2 siblings, boy and girl, at the age of 10 and 6 weeks. The family history is unremarkable except for consanguinity 5 generations previously. The clinical symptoms of the 2 patients conformed to the known features of AE, the gastrointestinal involvement loosing its significance with increasing age. In one patient in a stage of exacerbation the serum level of oleic acid (18:1) was lowered and of linoleic (18:2) acid slightly increased while that of arachidonic acid was decreased (Fig. 4). In both patients the serum zinc levels were significantly lowered. Under substitution with ZnSO4 the clinical condition improved and the serum zinc levels returned to normal. Histologically the small bowel mucosa was practically normal. Ultrastructural examination of jejunal biopsies revealed rather unspecific changes in the enterocytes in the form of numerous multivesicular bodies. The Paneth cells sometimes contained irregularly formed inhomogeneous structures within their cytoplasm. In addition the secretory granules varied in size and displayed a granular heteromorphic matrix. Frequently they were confluent and formed giant granules.