The relevance of secondary radicals in the mode of action of anthralin

The formation of free radicals during the reaction of anthralin analogues with peroxidizing polyunsaturated lipids was monitored by ESR spectroscopy. The biological effect of the different compounds was assessed by their ability to inhibit respiration of cultured human keratinocytes. C(10)-monosubstituted analogues of anthralin exhibited a strong antirespiratory effect and produced a cascade of radicals. Abstraction of the hydrogen atom at C(10) led to the generation of primary radicals which further decomposed into secondary radicals similar to those observed with anthralin itself. 10, 10'-disubstituted analogues of anthralin did not form any paramagnetic species during reaction with peroxidizing lipids while decomposition of a 2,7-disubstituted anthralin derivative under the same conditions resulted in primary, but not secondary radical species. Since both types of disubstituted analogues are devoid of antirespiratory activity we postulate that the antimitochondrial and thus antiproliferative activity of anthralin and its analogues is associated with their capacity to form secondary radicals during their decomposition.     

Cytogenetic studies of mice exposed to styrene by inhalation.

The data for the in vivo genotoxicity of styrene (STY) are equivocal. To evaluate the clastogenicity and sister-chromatid exchange (SCE)-inducing potential of STY in vivo under carefully controlled conditions, B6C3F1 female mice were exposed by inhalation for 6 h/day for 14 consecutive days to either 0, 125, 250 or 500 ppm STY. One day after the final exposure, peripheral blood, spleen, and lungs were removed and cells were cultured for the analysis of micronucleus (MN) induction using the cytochalasin B-block method, chromosome breakage, and SCE induction. Peripheral blood smears were also made for scoring MN in erythrocytes. There was a significant concentration-related elevation of SCE frequency in lymphocytes from the spleen and the peripheral blood as well as in cells from the lung. However, no statistically significant concentration-related increases were found in the frequency of chromosome aberrations in the cultured splenocytes or lung cells, and no significant increases in MN frequencies were observed in binucleated splenocytes or normochromatic erythrocytes in peripheral blood smears.     

The challenge hypothesis: Where it began and relevance to humans

A contribution to a special issue on Hormones and Human Competition.Over 40 years ago assay methods that allowed the accurate measurement of circulating levels of hormones were developed for the first time enabling us to sample free-living as well as captive animals. This led to a new concept called “field endocrinology”. It quickly became apparent that endocrine profiles of animals under natural conditions were very different from congeners in captivity. Furthermore, hormone data could be organized by functional units (e.g. reproductive states) spaced in time according to natural duration of those states rather than simply by date alone. This approach changed how we interpret data and revealed species-specific patterns of hormone secretion. The “challenge hypothesis”, stating that the temporal patterns of testosterone in blood were determined by a trade-off between the degree of male-male competition that increased testosterone, and the expression of paternal care that required a decrease in testosterone, grew out of a combination of field endocrine investigations that then informed laboratory experimentation. A strong argument can now be made that the challenge hypothesis is highly relevant for understanding social interactions in humans and non-human primates. Investigations on human subjects provide some of the best models for the challenge hypothesis. However, the central mechanisms by which aggressive and other social interactions regulate the hypothalamo-pituitary-gonad axis will depend upon work on not only primates, but also other vertebrates in very different ecological contexts. Research on the challenge hypothesis in humans will play a critical role as new insight on the interrelationships of testosterone and male-male competition comes from new technologies.     

Structural and mode of action studies on bio-active molecules

The technique of nuclear Overhauser effect difference spectroscopy allows the determination, from¹H nuclear magnetic resonance spectra, of those protons in a structure which are near in space to a selected, irradiated proton. The experiment is extremely powerful in the determination of structure in solution, and is sufficiently precise often to give stereochemical detail. The method was used in determination of the structures of the antibiotics of the teicoplanin complex (members of the vancomycin group), and the principles are briefly illustrated. Additionally, nuclear magnetic resonance pulse sequences can be used to edit¹³C spectra (separate the spectrum into four spectra, containing C, CH, CH₂, and CH₃ carbons), and this technique also aided the structure elucidation of the teicoplanin complex. Finally, it is emphasised that nuclear Overhauser effect difference spectroscopy can be used to determine the molecular details of drug binding sites, and an example is given.     

Atrazine and reproductive function: mode and mechanism of action studies

Atrazine, a chlorotriazine herbicide, is used to control annual grasses and broadleaf weeds. In this review, we summarize our laboratory's work evaluating the neuroendocrine toxicity of atrazine (and related chlorotriazines) from an historic perspective. We provide the rationale for our work as we have endeavored to determine: 1) the underlying reproductive changes leading to the development of mammary gland tumors in the atrazine-exposed female rat; 2) the cascade of physiological events that are responsible for these changes (i.e., the mode of action for mammary tumors); 3) the potential cellular mechanisms involving adverse effects of atrazine; and 4) the range of reproductive alterations associated with this pesticide.     

Application of conductance measurements to drug mode of action studies

The cytotoxic properties of 1-(2-nitro-1-imidazolyl)-3-(1-aziridinyl)-2-propanol (RSU-1069) on wild-type Escherichia coli and mutants defective in specific DNA repair have been studied. Comparison of the conductance curves obtained for each mutant strain with various drug concentrations allows determination of the processes involved in the repair of drug-induced damage and from this the type of damage induced may be determined. Automated conductance measurements can be used as a model system for studying modes of drug action.     

The relevance of cryoprotectant "toxicity" to cryobiology

Cryoprotective agents are essential for the cryopreservation of almost all biological systems. These additives, however, do not usually permit 100% survival after freezing and thawing, though from a theoretical point of view they should be able to fully suppress all known types of freezing injury. In view of the known biological and physicochemical effects of cryoprotectants, it is suggested that the toxicity of these agents is a key limiting factor in cryobiology. Not only does this toxicity prevent the use of fully protective levels of additive, but it may also be manifested in the form of cryoinjury over and beyond the cryoinjury due to classical causes. Evidence for this extra injury ("cryoprotectant-associated freezing injury") is reviewed. It is suggested that better suppression of toxicity is possible and will lead to advances in cryopreservation.     

Histological studies on the vaginal plate and vaginal epithelium in androgenized rats

Summary The present work is a histological study on the epithelium of the vaginal plate and vagina proper of intact rats, 5–45 days old, and of rats which were injected with 1.5 mg testosterone propionate at the age of 5 days (androgenized) and studied at different ages from 6–45 days. Moreover, the vaginal epithelium in adult androgenized rats was studied.A perforation of the vaginal plate and an external orifice of the vagina was seen in intact rats about 35 days old. The perforation resulted from cornification in scattered, later confluencing, regions in the epithelium of the plate.The androgenized rats developed a precocious vaginal opening at 12 days of age. Also in these animals the perforation of the plate resulted from a cornification in the center of the strongly thickened plate. After a lumen had developed the plate region presented a transitional epithelium. This was transformed into a stratified squamous epithelium at about 35–45 days, that is when the first oestrus occurred in intact controls. In contrast to the strong reaction to testosterone in the epithelium of the vaginal plate no effects could be seen in the vaginal epithelium proper, with the exception of some leucocytic infiltration.The adult androgenized rats had a cornified vaginal epithelium which in two cases showed some leucocytic infiltration. Acknowledgement. This investigation was supported by grants from the Swedish Medical Research Council (no 14X-571-02 and no Y 479) and from the Swedish Cancer Society (no 64164).