Gisela Witz

Biological interactions of α,β-unsaturated aldehydes

Abstract This article describes the chemical nature of α,β-unsaturated aldehydes and some of their toxicological effects based on their ability to function as direct-acting alkylating agents. Selected compounds discussed include α,β-unsaturated aldehydic environmental pollutants, metabolites of xenobiotics and natural products, and lipid peroxidation—and DNA oxidation products derived from cellular constituents. Briefly reviewed are sources and mechanisms of formation of the aldehydes, their reactivity with respect to glutathione and amino-groups, their toxicity based on interaction with sulfhydryl and amino targets in cells, and modulation of their toxicity by metabolism.

Stimulation of human polymorphonuclear leukocyte superoxide anion radical production by tumor promoters

Comparison was made of the ability of the potent tumor promoter phorbol myristate acetate (PMA), as well as less active PMA analogs and non-phorbol ester tumor promoters, to stimulate superoxide anion radical (O-.2) production by human polymorphonuclear leukocytes (PMN). The rate of O-.2 production was found to correlate with the tumor-promoting activity of the phorbol esters as opposed to their inflammatory activity. Mezerein and telocidin B were slightly better stimulators of O-.2 production than PMA. Acetic acid was inactive. These data are discussed in terms of a possible role for O-.2 and other reactive oxygen species in tumor promotion.

Retinoid inhibition of superoxide anion radical production by human polymorphonuclear leukocytes stimulated with tumor promoters

Abstract All-trans retinol, retinyl acetate and retinoic acid were found to be effective inhibitors of O 2 − • polymorphonuclear leukocytes stimulated with the tumor promoter phorbol myristate acetate. Retinol similarly inhibited cells stimulated with mezerein or teleocidin B. No-effect concentrations of the protease inhibitor antipain potentiated the inhibitory effect of low levels of retinol. Higher concentrations of retinol and antipain resulted in an additive or less than additive inhibitory effect.

FREE RADICALS AND CARCINOGENESIS

The role of free radicals and active states of oxygen in human cancer is as yet unresolved. Various lines of evidence provide strong but inferential evidence that free radical reactions can be of crucial importance in certain carcinogenic mechanisms. A central point in considering free radical reactions in carcinogenesis is that human cancer is really a group of highly diverse diseases for which the initial causation and the progression to clinical disease occur through a wide variety of mechanisms. Furthermore, for many human cancers it appears that there are alternate pathways capable of tumor initiation and tumor progression. While for certain of these pathways free radical reactions appear necessary, it is unlikely that there are human cancers for which free radicals, or any other mechanism, are sufficient for the entire process beginning with the genetic alteration leading to a somatic mutation and eventually resulting in clinically overt disease. It is crucial that we view free radical reactions as among a panoply of mechanisms leading to human cancer, and consider research about the role of free radicals in cancer as opportunities to prevent the initiation or progression of human cancer.

Enhancement of rat and human phagocyte superoxide anion radical production by cadmium in vitro

The mechanism by which cadmium produced oxidizing effects in vivo is unknown. We show that cadmium enhances the production of superoxide anion radical (O-(2) .), a reactive oxygen species, in digitonin-stimulated phagocytes from man and rat. Cadmium concentrations ranging from 3.6 X 10(-2)M to 3.6 X 10(-4)M inhibited O-(2) . production in rat alveolar macrophages or human granulocytes. However, when activated in the presence of 3.6 X 10(-5)M cadmium, the production of O-(2) . was increased by a factor of 2.11 +/- 0.25 above control levels in human granulocytes and 3.6 +/- 0.62 above control levels in rat alveolar macrophages. This effect by levels of cadmium within the range of those occurring during in vivo toxicity might provide an explanation for the oxidizing effects of this metal ion.

Short-term toxicity of trans, trans-muconaldehyde

Toxicological and biochemical effects of muconaldehyde, a six-carbon diene dialdehyde, were evaluated in 6- to 9-week-old CD-1 male mice. The LD50 of trans,trans-muconaldehyde was 6.7 and 7.1 mg/kg body wt when calculated by two different methods. Administration of trans,trans-muconaldehyde (2 mg/kg, ip) daily for 10 and 16 days resulted in a statistically significant decrease in red blood cell count, hematocrit, hemoglobin, bone marrow cellularity, and hepatic total and free sulfhydryl content. There was an increase in white blood cell count and spleen weight at 16 days. Similar effects, but of much lesser magnitude, were observed when the mice were given the same total dose of 2 mg/kg divided into three daily ip injections of 0.67 mg/kg trans,trans-muconaldehyde for 10 and 16 days. This alpha,beta-unsaturated aldehyde is a potent bone marrow toxin in mice.

The Reactivity of Selected Acrylate Esters toward Glutathione and Deoxyribonucleosides in Vitro: Structure-Activity Relationships

Acrylate esters are alpha,beta-unsaturated esters used as plastic monomers whose toxicity may involve reaction with tissue nucleophiles via Michael addition. Structure-activity relationships for reactivity of selected esters with glutathione (GSH) and deoxyribonucleosides were investigated in the present studies. The esters investigated were methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, tetraethyleneglycol diacrylate, tetraethyleneglycol dimethacrylate, and ethyleneglycol dimethacrylate. To compare their reactivities toward GSH, esters were incubated for up to 1 hr at 37 degrees C and pH 7.4 with either GSH or red blood cells in phosphate-buffered saline followed by measurement of free thiol. In both systems acrylate electrophilic reactivity decreased with alpha-methyl substitution; however, the decrease in electrophilic reactivity was more evident in the cell-free system than in the red blood cell model. Increased alcohol chain length moderately affected the apparent second-order rate constant for the spontaneous reaction of acrylate esters with GSH, but did not affect potency relative to cellular GSH depletion. The apparent second-order rate constants of bifunctional esters are more than twice the rate constants of the much smaller monofunctional esters. Ethyl acrylate, a reactive acrylate ester based upon glutathione alkylation, has been designated a class 2B (suspect human) carcinogen by the International Agency for Research on Cancer. To detect possible DNA alkylation by acrylate esters in vitro, ethyl acrylate was incubated with deoxyribonucleosides for up to 24 hr at pH 6.7 or 7.4 and 37 degrees C or up to 8 hr and 50 degrees C. HPLC analysis revealed no detectable adduct formation.(ABSTRACT TRUNCATED AT 250 WORDS)

High-performance liquid chromatography analysis of the thiobarbituric acid adducts of malonaldehyde and trans,trans-muconaldehyde

A reversed-phase HPLC method is described for the separation and analysis of the thiobarbituric acid (TBA) adducts of the reactive aldehydes muconaldehyde (MUC) and malonaldehyde (MDA). The TBA adduct of malonaldehyde was synthesized, purified, and its structure elucidated, for use as standard in quantitative HPLC studies. A detection limit of 1 X 10(-14) mol was achieved for the MUC:TBA and MDA:TBA adducts using the double monochromator fluorometric detector, 7 X 10(-13) mol was the detection limit using a variable wavelength uv-visible detector. Direct on-line identification of the eluting aldehyde:TBA adducts was achieved by the use of a diode-array uv-visible detector. The chromatographic behavior of the adducts under different mobile phase conditions was also examined. This HPLC methodology was used for the identification of muconaldehyde as a product of benzene oxidation in a hydroxyl radical generating system.

Decreased superoxide anion radical production by rat alveolar macrophages following inhalation of ozone or nitrogen dioxide.

Abstract In vivo exposure of rats to ozone or nitrogen dioxide results in a dose-dependent decrease in superoxide anion radical production (O 2 − ·) by alveolar macrophages isolated from the exposed animals. When alveolar macrophages from ozone-exposed animals were stimulated with phorbol myristate acetate (PMA, a non-phagocytic stimulus of O 2 − · production) the decrease in O 2 − · production ranged from 85.9% of control at 3.2 ppm-hrs ozone to 7% of control at 10.5 ppm-hrs. In a similar fashion, O 2 − · production by PMA-stimulated macrophages from NO 2 -exposed rates ranged from 78% of control at 18.3 ppm-hrs NO 2 down to 14.5% of control at 51 ppm-hrs. Since the viability of the alveolar macrophages obtained from ozone or nitrogen dioxide-exposed animals was 88% or better in all cases as judged by both Trypan blue exclusion and lactate dehydrogenase release, the decreased ability of these cells to produce superoxide anion radical cannot be attributed to a pollutant effect on cell viability. This diminution in superoxide anion radical production by alveolar macrophages from the pollutant-exposed animals might account, in part, for the ability of these 2 air pollutants to potentiate bacterial infections in laboratory animals.

Muconaldehyde, A Potential Toxic Intermediate of Benzene Metabolism

The metabolite of benzene that is responsible for its hematological toxicity is unknown. Benzene is of course the parent aromatic hydrocarbon and mush attention has been focussed on classical pathways of aromatic hydrocarbon metabolism in the search for toxic benzene metabolites. Elegant studies by a number of groups, including work presented at this symposium by Snyder, Irons, and Tunek, have evaluated metabolites such as benzene oxide, catechol, phenol, hydroquinone and their derivatives (See reviews by Snyder et al, 1977; Laskin and Goldstein, 1977). While there are some interesting clues concerning potentially toxic intermediates, and much important information has been obtained, the metabolic pathway and agent(s) responsible for the hematological toxicity of benzene remains unidentified.