Inhibition of Schistosoma mansoni ether-a-go-go related gene-encoded potassium channels leads to hypermotility and impaired egg production.

The purpose of this work was to investigate the effect of ether-a-go-go related gene (ERG) potassium channel inhibition on Schistosoma mansoni. Use of dofetilide to block the schistosome ERGs resulted in a striking 'corkscrew' effect. The worms were unable to control their motility; they were hypermotile. The treated worms produced abnormal eggs, some of which consisted of little more than a spine. One of the S. mansoni ERGs (SmERGs), Smp_161140, was chosen for further study by RNAi. The transcript was knocked down to 50% compared to the controls. These RNAi-treated worms demonstrated seizure-like movements. In S. mansoni, as in other organisms, ERG channels seem to play a role in regulating muscle excitability. This work shows that egg production can be greatly reduced by effectively targeting muscle coordination in these important parasites.

Maternal metabolism and teratogenesis in zinc-deficient rats.

Embryos removed at 11.5 days gestation from pregnant rats allowed a zinc-deficient diet from the time of mating showed a high frequency of malformations of all organ systems. There were, however, large differences between litters of individual dams. Comparison of the daily food intake of zinc-deficient dams with the appearance of the embryos suggested that fluctuations in the maternal serum zinc levels induced by feeding or fasting influenced the availability of zinc to the embryos. By cyclically feeding zinc-deficient dams to a predetermined schedule, low maternal serum zinc levels were induced at selected stages of development. This was accompanied by specific malformations of the organs developing at that time.

Zinc deficiency and the developing embryo.

The effect ofin utero zinc deficiency on fetal development in rats is reviewed. Attention is paid to the primary biochemical lesion associated with zinc-related teratogenesis and special consideration is given to the central nervous system. Evidence is presented that the thymidine kinase salvage pathway, used for the synthesis of thymidine monophosphate in DNA synthesis, is depressed more in fetal brain tissue than in the liver. In addition, greater reliance appears to be placed on this pathway than onde novo synthesis in the fetal brain than in other tissues. Some consideration is given to the use of in vitro embryo culture in studies relating to neurogenesis, but evidence is presented of a greater capacity of explanted rat embryos to obtain zinc from maternal serum than occurs in vivo.The rapid onset of a teratogenic zinc deficiency following dietary zinc restriction is again highlighted and further studies are described which demonstrate the critical impact of a single feeding cycle, of 4 d duration, on maternal plasma zinc levels and on the extent and nature of the observed fetal abnormalities. Evidence is presented that by shifting the timing of the high dietary intake/low plasma zinc peak to coincide with a particular 48 h period between days 6 and 10 of pregnancy, the pattern of malformations thus obtained reflected the coincidence of the high dietary intake of zinc-deficient diet and the critical time of morphogenesis of several organ systems.Whereas diminished plasma zinc levels at term in zinc-deficient animals are generally well correlated with reduced growth and dysmorphogenesis of the offspring, the same is not always found in human studies. In some cases, elevated plasma zinc levels at parturition are found in mothers with growth-retarded children, or vice versa. Experimental studies with rats are reported that suggest that maternal zinc status at term may be higher in dams bearing pups stunted by exposure to a transient zinc deficiency early in pregnancy, which in turn may have reduced the demand for maternal zinc in the later stages of gestation.The protective effect of zinc on cadmium-induced teratogenesis is discussed, particularly in relation to findings concerning an interaction of these metals in the embryonic yolk sac and thus on preplacental embryonic nutrition. Possible interactions between alcohol and zinc deficiency are also considered and data are presented pointing to increased fetotoxicity and teratogenesis in the presence of both treatments and to a more specific interaction with respect to reduced cell numbers in the developing rat hippocampus. Malondialdehyde levels, which reflect the extent of lipid peroxidation in tissue, are reported to be substantially higher in microsomes from fetal rat livers whenin utero deficiency and gestational alcoholism are combined. The suggestion is made that alcohol and zinc deficiency act independently in the body, but overlap to some extent at the common biochemical locus of membrane lipid peroxidation.

Interactions of cadmium and zinc in cultured rat embryos.

Rat embryos were cultured in serum taken from animals dosed with cadmium, or serum with cadmium added in vitro in the presence or absence of additional zinc. Embryos explanted at day ten and grown in serum taken from animals sooner than 4 h after dosing had a reduced DNA content after 24 h culture. In one-hour serum, the yolk sac had become thick and brittle. Zinc ameliorated the effects but had no stimulatory effect on post eight-hour serum when serum zinc levels were at their lowest. The hypothesis that cadmium induces a maternal zinc deficiency sufficient to cause teratogenic changes could not be sustained. Embryos explanted at nine days were much more susceptible to cadmium added in vitro than ten-day embryos. The principal anomaly, apart from a reduced DNA content, was a thickening of the yolk sac similar to that seen in embryos grown in serum taken from animals one hour after cadmium dosing. Addition of zinc to the medium prevented both of these effects. The suggestion is made that the cadmium-induced dysgenesis of the yolk sac precludes appropriate embryonic nutrition.

Inhibition of rat yolk sac pinocytosis by cadmium and its reversal by zinc.

The effect of cadmium on the in vitro pinocytic rate of 10- and 11-day-old rat yolk sacs grown on rat serum in culture was studied using the synthetic substrate 125I-labeled polyvinylpyrrolidone. In medium containing concentrations of added cadmium similar to those achieved in serum by intraperitoneal dosing of rats, the rate of pinocytosis in vitro was decreased by up to 55%. When zinc was included in the medium as well, the effect of cadmium was markedly reduced, and the rate of pinocytosis was restored to about normal. The results of this in vitro study suggest that cadmium can limit and supply of nutrients to the rat embryo in a nonspecific manner, and that elevated levels of zinc can restore the ability of the yolk sac to accumulate substances from the surrounding medium. Whereas cadmium may act as a teratogen at a number of sites, the demonstrated effect of this metal on the yolk sac provides a new insight into what could be a primary mode of action of cadmium on fetal development.

Superoxide dismutase (EC 1.15.1.1), manganese and the effect of ethanol in adult and foetal rats.

1. The activity of manganese-superoxide dismutase (EC 1.15.1.1; SOD) was increased in the livers and kidneys of adult rats after exposure to aqueous ethanol (200 ml/1) for 32 weeks. 2. The concentration of Mn in the livers and kidneys was significantly higher after 24 weeks, and by 32 weeks liver copper and zinc levels were lower. 3. The activity of foetal (day 19) liver superoxide dismutase was appreciably higher in offspring from dams receiving ethanol during pregnancy. Quantitatively the response appeared to be almost entirely due to the Mn-SOD form of the enzyme. 4. Maternal alcoholism during pregnancy had no effect on the levels of Cu, Mn or Zn in foetal (day 19) livers.

Postnatal accumulation of zinc by the rat hippocampus.

Timm's staining material has been detected in the rat hippocampus as early as day 1 postnatally. However, staining was diffuse and widespread and light granulation was observed only in the mossy fiber layer. By day 6 postnatally most diffuse staining had disappeared and the characteristic pattern of granulation had intensified in the mossy fiber layer. Pronounced staining of the mossy fibers became apparent from day 6.Electron microscopic autoradiography indicated that(65)Zn injected intraperitoneally into suckling pups became localized largely in the axons and axon terminals of the mossy fiber layer in the CA3 and CA4 regions of the Horn of Ammon.In vitro studies with hippocampal slices have demonstrated that zinc is accumulated by an active transport system, but the kinetic characteristics of this uptake do not appear to alter with age. Zinc located intracellularly in the hippocampus appears to be associated mainly with large molecular weight ligands, with more than 75% of newly acquired zinc being bound to substances having molecular weights greater than 70,000 Daltons.

High plasma zinc levels following oral dosing in rats and the incorporation of 3H-thymidine into deoxyribonucleic acid in rat fetuses.

In fasted rats, a single oral dose of zinc, equivalent to the total daily zinc intake, caused plasma zinc levels to rise about five-fold 1.5 h after treatment. Higher values were obtained following higher dose levels. At maternal plasma zinc levels approximately 10-fold above normal, fetal viability was disturbed and incorporation of 3H-thymidine into DNA became impaired in fetal (20-d) rat brain and liver tissue.

The effect of ethanol and acetaldehyde on DNA synthesis in growing cells and on fetal development in the rat.

Incorporation of 3H-thymidine into DNA was significantly diminished by treatment with ethanol and acetaldehyde in regenerating rat liver, rat cells in culture, and rat fetal tissues. Reduced incorporation was especially marked in the fetal central nervous system and was observed with both compounds at levels similar to those reported to occur in human alcoholics. The reduced incorporation of 3H-thymidine into fetal DNA, together with the increased fetal mortality observed in dams treated specifically with acetaldehyde during pregnancy, suggests that acetaldehyde is implicated in the mechanism of teratogenesis associated with the fetal alcohol syndrome.

Incorporation of(3)H-thymidine into DNA and the activity of alkaline phosphatase in zinc-deficient fetal rat brains.

The incorporation of(3)H-thymidine into DNA in the brains of the 17-day and 20-day old rat fetuses was significantly reduced by maternal zinc restriction during pregnancy. The activity of the enzyme thymidine kinase (EC 2.7.1.21) was similarly reduced in the zine-deprived fetal brains on days 14 and 20 of gestation, but not on day 17. Fetal brain alkaline phosphatase (EC 3.1.3.1) was significantly depressed by maternal zinc deprivation on days 17 and 20 of pregnancy.The data suggest an association between thymidine kinase and the reduced incorporation of(3)H-thymidine into DNA in the brains of 20-day old fetuses but not in animals on day 17. Alkaline phosphatase was however depressed at this stage.The suggestion is made that because of the complexity of brain development, future biochemical studies in this area should concern specific structures in the brain at particular critical stages during neurogenesis.