Self-labeling of human polymorphonuclear leucocyte myeloperoxidase with125iodine

In order to obtain a radioimmunoassay (RIA) technique for the measurement of human plasma myeloperoxidase (MPO), we purified the enzyme from polymorphonuclear granulocytes (neutrophils), and compared three methods of labeling it with¹²⁵Iodine: chloramine T, lactoperoxidase, and an original technique of self labeling based on the ability of the enzyme to oxidize and bind¹²⁵I in the presence of H₂O₂. The chloramine T technique produced a degraded protein, as well shown by a high non-specific binding of tracer to antibody. The lactoperoxidase technique did not succeed in labeling MPO with an adequate specific activity. In contrast, the self-labeling method gave a stable tracer with a specific activity of 23 Ci/gmg MPO (85 MBq), a satisfactory level of immunoreactivity, and a low-specific binding (3%). After labeling, purification of tracer was achieved by gel filtration chromatography in phosphate buffer (0.05 M; pH7) to which 0.1% poly-L-lysine was added. The labeled molecule remained stable for 40 days and could be used for RIA with a polyclonal antibody raised in rabbits.     

Disruption of mitochondrial function as the basis of the trypanocidal effect of trifluoperazine onTrypanosoma cruzi

Summary The tricyclic anti-calmodulin drug trifluoperazine (TFP) inhibited growth and motility of epimastigotes ofTrypanosoma cruzi, at concentrations lower than 100 M, and motility and infectivity of the bloodstream trypomastigote form at 200 M. Electron microscopy of TFP-treated epimastigotes showed that the major effect was at the mitochondrial level, with gross swelling and disorganization. The oligomycin-sensitive, mitochondrial ATPase was completely inhibited by 20 M TFP, and the same drug concentration caused a 60% decrease in intracellular ATP content. The results suggest that the trypanocidal effect of TFP may be related more to mitochondrial damage than to the well-known anticalmodulin effect of the drug.     

Effects of a change in the level of inbreeding on the genetic load

"The effects of inbreeding may not be as noticeable in the first generation as the invigoration immediately apparent after crossing". This statement, published in 1919, has received little attention, and has apparently never been tested empirically, although the reduction of the genetic load of populations by inbreeding is well known in theoretical terms. Because inbreeding increases homozygosity, and hence the effectiveness of selection against recessive or partially recessive detrimental alleles, changes in levels of inbreeding can lead to a reduction in the frequencies of such mutant alleles. This results in equilibration at higher population mean fitness and is referred to as 'purging' populations of their genetic load. Severe inbreeding can also reduce genetic load due to overdominant alleles, provided selection coefficients are not symmetrical at all loci, because alleles giving lower fitness will be reduced in frequency at equilibrium. With either fitness model, however, reduction in genetic load takes time, and the initial effect of an increase in inbreeding is reduced fitness due to homozygosity. There are few data relating to the extent to which fitness is reduced during inbreeding in a set of lines and to how long the reduction lasts before increasing again to the initial level, or higher. Inbreeding experiments involving sib mating in mice and Drosophila subobscura, and successive bottlenecks in house flies have yielded some evidence consistent with the purging hypothesis. Here, we report results of an experiment demonstrating a prolonged time-course of recovery of mean fitness under self-fertilization of a naturally outcrossing plant, and also compare our results with expectations derived by computer calculations. Our results show that the genetic load present in an outcrossing population can be explained only with a high mutation rate to partially recessive deleterious alleles, and that inbreeding purges the population of mutant alleles.     

Genetic factors in neurotoxicology and neuropharmacology: A critical evaluation of the use of genetics as a research tool

Animals have evolved a detoxication system to enable them to survive in a hostile chemical environment in which foods contain many non-nutrient chemicals. Detoxication depends on enzymes which are often genetically polymorphic. As a result, inter-individual variation is common, and in humans several Mendelian loci have been identified. However, most variation in response is probably due to the action of several genes. Genetic variation in response to the neurotoxin MPTP and to chemically and physically-induced seizures is reviewed. In the former case, differences between pigmented and white mouse strains have been noted which are consistent with the hypothesis that humans are more sensitive than mice or rats because of the presence of melanin in human brains. However, variation in sensitivity probably also depends on other genes. In the case of audiogenic seizures, a single locus has been identified and mapped, but its relationship with seizures induced by other agents is not clear. Genetic variation in response to alcohol is also discussed. The failure of most toxicologists to consider genetic variation as a potentially confounding variable, and as a powerful research tool, is discussed critically in relation to non-repeatability of research on the neurotoxic effects of lead, and in relation to the genetic variation in MPTP, seizures, and alcohol response already noted. It seems clear that genetic methods provide a powerful research tool which is largely being ignored by toxicologists.     

Tamoxifen ‘sex reverses’ alligator embryos at male producing temperature,but is an antiestrogen in female hatchlings

Summary Tamoxifen is an anticancer drug widely used in the treatment of estrogen-dependent breast cancer. In hatchling alligators it acts as a pure antiestrogen in that it completely blocks the effect of estradiol-induced oviductal hypertrophy and completely blocks the estradiol-induced hepatic vitellogenin secretion. Paradoxically, when injected into alligator eggs incubated at 33°C, a temperature which would normally result in 100% male hatchlings, tamoxifen sex reverses the embryos into apparently normal female hatchlings.